'98 7.4L Running lean - Can't figure it out

[mrZ71man]

So my bro has been messing with his truck for months now and we just can't seem to nail down what is going on. Truck is a 1998 C3500 with the Vortec 454. He bought it in October with the factory 4L80E that was slipping badly. He swapped it out for an NV4500. He is getting the lean codes (p0171 & 0174) and even after all the parts he's replaced and tuning done to the computer he can't stop the Long Term Fuel Trims from climbing to 25 as soon as the truck goes closed loop. In open loop it runs fine and FT's are between 0-5. Truck does not run particularly well and gets bad fuel milage (~9).

Here's whats been replaced: Upper & lower intake manifold gaskets, MAP sensor, vacuum lines (FPR to intake and IAC to emission canister), PCV valve, #3 & #8 injectors as they were registering low flow, plugs, wires, cap, rotor, MAF sensor, thermostat, all O2 sensors, ran 4 gauge grounding straps from battery to body & frame to block because we had a weird grounding issue while we tested resistance in the wires on the MAF & O2 circuits. Those circuits had no significant resistance by the way. Tune loaded in the computer is out of a '98 with the big block & 5 speed so thats good. We played with the Hz values in the MAF circuit with EFI live and bank 1 did improve but bank 2 still maxes out at 25.

Looking to see if anyone else has ran into an issue like this before. Thanks.

[TexasT]

I don't see where you addressed any fuel system pieces. Fuel pump, FPR, new filter, new set of injectors. I do see where you put two new ones in but the rest of the old ones could be leaky. Those stock injectors are known to be leaky as mileage of the vehicle rises.

What is your fuel pressure koeo, idling and when you rev the engine/drive the vehicle?