5.3 Gen 3 - Misfire/rough idle

[AnimalMother]

I just purchased a 71 C10 that has a 5.3/4l60 swap, BTR stage 3 cam w/ LS6 springs. The truck has a misfire with an intermittent CEL. I should also state that the wiring of this engine was done haphazardly, to the point in trying to connect a code reader to the OBDII port a couple of wires sparked together.

The engine starts and runs, but under any load it stutters at wants to die. I've checked for vacuum leaks with MAF cleaner sprayed around the intake and TB while running, checked all plugs/wire and all cylinders are firing, just looking for any other suggestions before I start throwing parts at it. I'm also planning to buy a new harness for it to replace the spliced and gutted harness that it currently being utilized, which could be the problem all together. Appreciate any help.