Sluggish throttle response low power

I have a 95 camaro Z28 350lt1 "P" code motor 125000 miles I purchase the car from a kid who ran it hot. I have replaced the Timing chain, Oil Pump, water pump, distributor, wires, plugs, heads, coil, O2 Sensors, ignition control module, all hoses, belt, cleaned the injectors, checked the fuel pressure which is fine. no codes showing, system scan shows everything working properly, I'm a little Leary of the mass air flow sensor which I cleaned with the new spray cleaner. pulling wire off throws a code for it. after i replaced the ignition system the cars ran great for awhile, then after a few burn outs it just had no power. I was told that it might have jumped timing so i check the chain and it was loose so i replaced the timing chain and gears. the only item that is not stock on the car is headers they also glow red when trying to rev up engine. #1 & 2 temperature are cooler than the rest, meaning that they don't glow red. Checked the EGR Valve it makes the car stumble at idle when vacuum applied. Car starts and idles great but you press on the gas pedal and it backfires and slowly builds rpm's. when it reaches higher RPM's it has good throttle response around 2 -3 thousand. Place the car in gear and won't pull itself. it idles at around 800-1000 RPM's. Plus now the car seems to run hot gauge shows 240 - 250 almost at the red line. Fans are working. Any suggestions would be greatly appreciated.