HELP NEEDED OBS LQ9 swap going into reduced engine power mode
 

92 k1500 with nv3500 swapped in a cammed, fully bolted LQ9, that is Nelson tuned and am using a stand alone harness. Drove the truck for around 50 miles no problem and then loss of throttle and it died. If I crank and crank and crank it will start and idle real rough for a few seconds and then turn off. All the while it has no throttle response. Every now and then it will crank and run/drive fine but if it is turned off then it will revert back to no throttle response/rough idle/no cranking. The codes that seem to be coming back are p0120, p0220, p1516, and p1125. I've done a lot of web research on the codes and have swapped out the pedal/app, throttle body/TPS, and the TAC with brand new units, vss is hooked up, double checked my grounds, added a ground from the block to the LS harness grounds location(driver side shock tower), verified with tuner that VATS had been disabled, and checked the voltage to the fuse block....still having the same issue. The voltage to the block with key on was 12.3ish, and while cranking was 10.8ish. Before I swapped in the new pedal, throttle body, and tac I ran through the procedures to check them with the multimeter and all was good. The p1516 or the p1125 will come back quick but the others have not yet....not that they wouldn't if I continued to try and crank it. Also, I am getting p0740, p0753, and p0785 transmission codes. I'm assuming because that PCM is set up for an auto trans and I have a manual. Could that be a contributing factor? It's strange because if I crank and crank and crank it it will eventually idle and drive fine but as soon as it is shut off it will be back to no pedal and not staying cranked. I appreciate all the help I can get on this.....I'm at a loss

Ended up solving it. Here's what I did you anyone that stumbles upon this thread. I had previously checked fuel pressure it but was trying to do it by myself and it seemed to be all good. I did it again tonight and it would prime to 50-55psi but as soon as I cranked it and it started it would loose pressure and stall. I ran a wire from my modified LS harness fuel relay to the gray power wire at the fuel pump and all seems to be good now! Looks like the new pedal, new throttle body and new TAC are getting returned lol