84 K10 Hates its New Exhaust: Help!

[SourTooth307]

Saturday afternoon I installed a custom exhaust system on my 84 K10 and now it runs awfully......

The truck was running with a set of Flowtech headers, and some flex pipe that ended right after the cab making for a pretty loud (and illegal in NJ) exhaust system. I added new Flowtech headers, two new Flowmaster universal cats, and two Dynomax super turbo mufflers with outlets ahead of the rear wheels. I also installed new AC Delco sparkplugs and wires since when ignition wires come off, they don't like to go back on.

Now I have a truck that pops, backfires, and sputters when you try to move it. It basically limps everywhere it goes and I'm not sure why. I'm hearing things like the timing, or the Edelbrock carb I have on it is the wrong application, but if all these things were true, why would it have ran beautifully before the change? I've never seen an exhaust system have this kind of effect on a vehicle before. Any help would be greatly appreciated. Thanks.