Jc1224

My car has a missfire under load and doesn't run right. I once got a po300. I changed maf,iat,ait,tps,oxygen sensors,plugs get fouled, changed wires for spark plugs, It started out of no where. I put a Magnuson tvs1900 had it tuned and a couple days later it started. To mechanics and $325 later have not found the problem. They say my coils are fine along with injectors. Everything is new even the lengthinfelter fuel pump at 67psi reading. Vacuum is at -20 . I don't think all then coil packs should be faulty as all the plugs are fouled. Check valve springs look ok. Car revs fine in idle but once in gear it dies