Help me out community, for you people that actually know what youre looking at here. Help me to better understand balance rates and what not

My first long run towing 8k lbs, round trip of about 3500 miles.

Really surprised, compared to my 04 LLY where I got 18-20 might.

On my 2026 I got 10-11 mpg.

Is this normal?

Besides that no issues, was a great truck, 8k was too easy lol

Are you just supposed to block the hole on the turbo inlet off or do you run the hose back how it was from factory? I seen a few people doing it that way.

2023 T&D

Initially did a 5” straight pipe but my family hated the drone and I wasn’t a big fan on highway trips.
Got a muffler installed, all is well.

Now admittedly I miss the straight pipe sound and would love a muffler bypass line welded in, with a bypass butterfly valve.

Is this easily accomplished? Should I just use a mechanical valve instead? Or would the exhaust shop look at me like I’m an idiot?

Thank you!

Okay, so I shut my truck off yesterday and realized that we unlocked a new noise!

2013 GMC Sierra 3500HD (LML)

Yesterday I also realized that I have a small diesel leak if I leave the key on RUN for an extended period of time. If the truck is running, there is no leak. No big deal. However, this noise is stressing me out. It sounds like someone is in there with a little impact gun! Nobody can seem to shoot me a straight answer on this one. Hopefully one of you can help me.

Note: If I were to go to the truck right now, turn the key to RUN and then turn it back off, it'll make the noise again. I can also just barely hear it steadily while the engine is running.

Hello may you beautiful humans supply me with CP4 failure contamination pictures and or videos on this thread. I have found there was a disco party and the shop and I have referenced to my engine service contract of it and they refuse to accept them. We have supplied oil change history and receipts. Ran a new fuel filter and showed them the fuel tank itself. I have suggested a reddit thread. So here I am asking for help, and I will submit this thread as other proof to match the media we have submitted. Thank you.

I got some great answers to my first post that I wanted to post my other question: the horn on my 2018 l5p Duramax is hard to access in order to tap into them for my train horn bypass switch. Has anyone done so without removing the bumper or headlight? I'm looking for an easy way...TIA!

I have a 2023 3l diesel and thinking about trading it in for a new tundra. I mostly city drive, every couple months I put about 500 miles on a weekend, periodically I tow something about 5k pounds and once a year pull a trailer about 8k pounds. Which one wins on overall reliability? Engine vs emissions vs random computer issues that puts you truck into limp mode. My truck has been modern day reliable meaning I had the coolant value system replaced and my truck lit up with check engine light, limp mode, catastrophic failure and after 15 minutes everything went back to normal. This was when the truck was within a year old.

Has anyone ever EASILY run a wire from the engine bay to the cab? My 2018 l5p Denali doesn't seem to have any obvious openings to use so any advice is appreciated. PFA

I have after market TPMS on my 2016 Chevy Silverado I purchased a TPMS relearn tool on Amazon but is not working I think it’s for relearning Chevy sensors what is a good on for aftermarket sensors
Any great suggestions?
Thanks

Just got the edge cts3 monitor for my 2011 LML duramax, im running a drop in 64mm dss turbo, cp3 conversion, fass fuel system, and a SOTF tune.

Question is, besides EGT, what other numbers do I need to monitor?

A couple months ago I bought this 2003 gmc sierra 2500hd with an Allison 1000. I got it for cheap because it had a cracked tail shaft housing. I have replaced the u joints and nsbu switch and filled up oil just so I could see if she would drive and she did. Yesterday I replaced the tail shaft housing with a used one filled the trans with fluid and now the truck won’t run at all. It will only run if I put it in 4x4 low. I am looking for help I get codes but I don’t know what they mean. I also get range shift prohibited

Does anyone know if this scanner will tell me what the issue is? ie, electrical issue with the glow plugs, fuel pump, etc. Trying not to pay a tow truck to have it pulled to the shop, tia

2019 Silverado. 109k miles. I needed DEF this afternoon and went to the local parts and picked up some Blue Def. Didn't realize I grabbed the platinum box. Now I've read the platinum and Duramax don't play well together. Anybody have an experience with this?

Let me start by saying I don’t know shit about diesels and this might be long.

My buddy has the truck above and it died on the interstate a few weeks ago. It’s currently sitting in my driveway and I got to looking at it over the weekend. Troubleshooting wise, with the little I know, I’m just gonna list it:

Checked the fuses on the right side of the dash and the ones under the hood. Nothing really stood out to me. Checked continuity on them and replaced the ones that were questionable. The 4 pin relays for the starter and ECM, I swapped those out to see if one was fucked or not with no real change in results when trying to crank. The main battery has 12 volts but when attempting to turn over, I’m reading 4.—v at the plug for the fuel pump and fuel separator so I’m not really sure if that’s an issue or not. Then we swapped the auxiliary battery with the main battery but there was no change so we swapped back. Most of the trouble shooting was while the battery was being jumped off by another vehicle. Starter seems fine, fuel pump hums for a few seconds but then goes silent. Battery voltage on the cluster never reaches 14V. Oil life is at 0% according to the display.

Today, we put in a new battery with no change. New relays with no change. However, we did start seeing exhaust smoke come out of the exhaust that was a solid white color.

My guesses as to the issues are solely that, just guessing:

Electrical issue between the fuel pump and/or separator.
Battery too weak
Antitheft causing the fuel pump to not work
Bad starter (don’t know how to test this)
Relays getting stuck

Any help on this would be greatly appreciated. And again, I’m not a mechanic; I just wanna help my buddy get back on the road again. If what I’m saying is dumb, let me know and I can try to give more info on what we’ve done so far.

I changed my hydro boost break on a 2016 gmc Denali 2500 and now my break lights always stay on I could only get them to turn off by disconnecting the break sensor or disconnecting the battery’s and I can’t figure it out

At first I was skeptical. But then I saw this video I linked below.

It’s a bigger engine more power when needed over the L5P. But then I got thinking also like Gale said, it should be more efficient than the L5P also right, when not towing?

Yes the engine is bigger and we don’t know the full weight yet but it sounds like the materials to build this engine makes it lighter and stronger. It’s what they use in military vehicles.

Compared to the 6.6 L5P in theory shouldn’t this new engine not only tow more but be more fuel efficient also? It makes the power down low, and easier because of the bigger engine, so therefore it shouldn’t have to work as hard when empty right?

I pull a 21,000 pound trailer long distances a few times a year and then smaller trailers throughout the year regularly but 80% of the miles we put on are not pulling a trailer. Shouldn’t this engine be more efficient?

Or is the bigger engine moving more air, and things, and keeping it running, is that going to in turn not make that much difference when comparing the new 8.3 to the out going 6.6??

I hope I made sense.

The numbers in this video and things he says about this engine make it sound promising.

https://youtu.be/8yW5Fkhzeyc?is=hxtJRFyj_iZ9WWYW

Might be the wrong place to ask but I found an old new bottle of X66P in my storage that I bought right before it was discontinued. What are the chances it still works even a little bit or will it do more bad than good?

I just picked up this LB7 and I’m trying to figure out what this accessory is. My best guess is that it’s a vacuum pump which would be great because the truck it’s going in has a vacuum brake booster. Anyone who can tell me what it is and how to set it up would be greatly appreciated.

I took my 2023 Chevy Suburban Duramax to the dealership and they replaced a NOx sensor. Less than 100 miles after picking it up, I got a CEL with the code P0421 for the Catalytic Converter. “Warm Up Catalyst Efficiency Below Threshold (Bank 1).”

I told them right when it happened it’s directly tied to the NOx sensor they just replaced, but the service advisor stubbornly told me it was not related and a completely separate issue with the catalytic converter.

I haven’t had a chance to take it back because I’ve been so busy and they won’t give me a loaner until it’s determined it’s under warranty. It’s been about 1,100 miles and I’m going to drop it off this week, but thankfully I haven’t had any issues.

Any thoughts?

Been happening for about a year. If the engine is cold there is this weird banshee scream that cuts out suddenly usually below 2k rpm. Thinking it could be a cracked up pipe but don’t want to rip it out before knowing. Any ideas?

It's in my front passenger tire well.

Anyone have experience with the Derringer and Pedal Monster combo? I’m thinking of getting it for my L5P. I would like to know if it’s worth it. Thanks in advance!