ok it is a 95 t5 dual exhaust car. it has a new holley fuel pump,plugs and wires and the air filter is clean. the mufflers fell off, so it that is hurting peformance i believe. it also has had one code that i know of and that is the header o2 sensor on the driver's side. i really don't think that has anything to do with it though. it has been on for a long time. anyway last night i was driving about 30 in a neiborhood and i thought i heard a faint backfire through the intake. well today i know i heard a backfire but i think it came from the exhaust. it sounded like a shotgun being fired from the car behind me. see, there was this dumb ****** zipping through traffic even though it is raining pretty badly on this busy 2 lane hiway. so i wasn't going to let that ignorant ass cut me off like she was doing to everybody else. she tried to pass me when there was no room so i dropped it into 4th and stepped on it. and it was running like it always does sluggish but leaving her behind and all of a sudden i heard this noise and i thought what in the hell is this thing backfiring for. i didn't know. somebody has a 4.2 liter truck that has been having the same problems as me.(sluggish,no power until high rpms and then it still has little, backfiring occasionally). they didn't know what was wrong so it went to the shop and the culprit was a worn out keyway that held the harmonic balancer in place and in time. and since the magneto is or whatnot is on the balancer and the 3.8 is the same thing basically as the 4.2 i think i may have something like that. i tried to take that off last week to check but the bolts i used to pull it off were bending. any ideas. the fuel filter is new and the injectors are some working spares i had on the original motor. it has a 2000 shortblock in it now.