Ok guys this is gonna be long but I will try and keep it as on topic as possible. Background: 300,000 miles on the motor, but it has 50psi oil pressure hot at 2000RPM and 20 at hot idle. I've owned this since it was new. Been a great truck. Valve covers had never even been off until recently. About 10 months ago bad head gasket. R&R all put back together no problem. Ran great put 6000 miles on it. Fantastic! Skip ahead ---> Missing a little at low RPM under load. Skipping a fire every once in a while. No biggie, DTC for a bad EGR valve. Installed new GM valve. Problem still there. Ok, next I start throwing parts at it. The following are brand new parts installed currently. EGR EGR solenoid Plugs Wires Cap Rotor New distributor New ignition module New 02 sensor New MAP sensor New coolant temp sensor New IAC valve New TPS sensor New fuel pressure regulator New injectors New fuel pump and sock New fuel filter New catalytic convertor New timing chain and gears Also tried a different (known good) tbi with the same results. edit: New GM ECM Now the funny part is that it ran ok, and would smoke the tires and idle perfectly. But when I got on the interstate it would start the same missing and now backfiring through the exhaust and manifold. But it was still running ok other than this. I let it sit for a week, and now it wont even start. WTF /forums/images/graemlins/confused.gif /forums/images/graemlins/angryfire.gif I have checked compression and get 140 +/- 4psi between all cylinders. It pulls 22" of vacuum at idle. Not bad for 300k miles. I got it to run a while later, but now, it runs terrible. Backfiring and such. The timing is Dead on right. The compression is still the same. Well come to present, I triued to start it and drive it around, I think I flooded it, so I was pulling plugs and broke one /forums/images/graemlins/doah.gif /forums/images/graemlins/doah.gif /forums/images/graemlins/angryfire.gif /forums/images/graemlins/angryfire.gif /forums/images/graemlins/doah.gif. So I need a new plug maybe all new plugs, cant hurt. /forums/images/graemlins/dunno.gif Any ideas from the gurus out there, or do I need a new engine. This truck has sentimental value, and being a 300k truck I am trying to hit 400k. I appreciate any responses I get, and thanks to all in advance. p.s. I may have left some parts or steps out. I will think of them as we go.