Ignition, Exhaust, Or ECM problem ???

Hello All, My 86 TA was running fine, then it began to stall and backfired. All power was lost and the backfire shredded my muffler. I had a strong crank as well as fuel delivery, but no spark. After replacing my coil, capacitor, and ign module; the car started fine and idled fine. However, when I go over 25 the car shudders and loses compression, sometimes stalling out. It starts up and idles without a problem.
I know the power won't be as good since my muffler is beat, but could it really make the car stall???? My Distributor cap, wires, and plugs are good. Maybe Timing??? ECM trying to compensate for something?? Any help would be much appreciated!!

86 FB Trans Am
305 4bbl
HEI

Sounds like two problems.....the first one was NO SPARK....OK you fixed that....
Backfires are usually caused by the spark firing during the exhaust stoke or a over rich condition building up gas flumes in the exhaust system in burning at one....
Make sure the plugs wire are routed correctly..check wire by wire to each plug.
Look for a cracked cap or moisture in the cap.
Timing...yes check it out!
Don't worry about the muffler blown out...that will not hurt a thing but more noise...
Does it have at Catalytic Converter? Also any chance of water in the gas???

[Thanks for the Reply. As it turned out, my carburetor was shot. Some Secondary spring was broke. Not bad though for 214,000 miles. Gonna cost me some change though since its computer controlled 4 bbl. Havin it rebuilt. see ya!

A fix is a fix that whats counts!!.....Good Luck!