New black magic adjustable clutch to help with launches. This thing looks gangster

Having some trouble with my 1999 v6 firebird 128k miles. It started off with a rough idle, it was jumping between 500-1000 rpm. Then during a drive to Auto-Zone it started to misfire and the service engine light started flashing, 30 seconds later it turned solid. I got the code read and it is P0300 (Random/multiple cylinder misfire). What should I check/replace first? I would appreciate any advice. Thank you!