I'm not sure if the fuel pump will solve the problem or not. The service bulletin does not cover my motor. I have a serial number 0M0xxxxx. Even though it is a 6.2, I've found some of the information in Service Manual 31 is accurate, but some of it is not, its instead accurate in Service Manual 24. One example is the wiring harness.

Getting back to trying to figure out this problem. Completely disassembled motor over winter just to triple check i put it together correct. Everything looked good. Got a suggestion to try leering it run for a long period of time. They said if water got in the lifters it could take an hour or more to clean them out. Didn't make sense, but tried anyway. Was only running on a couple cylinders, and barely at that, but i kept it running. By about 30 min, was running on 5-6 cylinders. Rather than keep running, i put in new lifters. It's now running 80% better, but still not perfect.

It doesn't seem to go into base timing mode. I use the rhinda software and select base timing mode, but it doesn't raise rpm as it should, and setting at 10deg BTDC doesn't give me the best running position.

With dist set to the best place it runs, at idle it sounds like it's still missing, then every once in a while it will pick up and sound great for a few seconds. Advancing the throttle does cause engine to speed up, but also causes backfiring.

Making progress...slowly.

if you have good compression on all cylinders and can,t seem to get it timed and it is backfiring it is lean.did you recheck the fuel pressure after replacing the pump.if it is not maintaining 43 lbs fuel pressure it will not run worth a chit.