My 5.0 runs like a 4 cyl - please help

I just bought a 1995 Mustang GT 5.0 convertible, Automatic Trans...looks great but runs like a 4 cyl. My family minivan out ran it! It idles ok, but when I take off it just doesn't want to go. It sounds like it is missing and it backfires (especially when it's cold). The check engine light comes on, it doesn't stay on, but it won't stay off either. I replaced the plugs, wires, distributor cap, fuel filter and the O2 sensors. It runs better but it still backfires and maybe now it runs like a 6 cyl. Does anybody have any suggestions on what to do next?[img]/phpBB/images/smiles/icon_confused.gif[/img]
[addsig]

Clean your MAF and check your timing. A bottle of injector cleaner probably wouldnt hurt either.

Make sure all the ignition is working properly as well. I've worked on 3 this year, 2 2.3's & a 4.6 that all had a bad coil pack.
[addsig]

get your hands on a code scaner and run the key on engine off test. that is almost always step one on these new fuilie cars. they are fairly cheap @ your local auto parts store good luck chris