Alright, so a few months back I let a friend take my car for a spin with a few people, so there was a bit of weight. He did a pull, got to the top of third and the engine gave out and misfired. Tried it again and it did the same thing. Driving home that night the car would occasionally misfire, and it progressively got worse. For the past few months the car's been off the road getting body work and paint, and just recently I got it back. If I drive out of boost there's no misfiring, but the second the gauge hits 0 and tries to build boost, misfires everywhere. Coded it and got P0300 (random multiple misfires) and a bad upstream o2 sensor.
Changed the o2 sensor, lost that code, and still have my misfire.
Put in NGK iridium spark plugs gapped to 22, 24, and 26 with nothing fixed.
Cam angle sensor was also replaced.
installed a friend's coil packs and wires; no difference.

I recently took the car into a shop and after fixing some boost leaks and wiring issues, the car still misfires. Right now they're not quite sure what to look into next, and I have no clue what's up...so I'm turning to you guys!

Car's running a Tomei m7960 with all supporting mods and makes 370WHP.

 

Did you check your fuel system? Mainly the injectors