2008 Chevy Silverado 2500hd 6.0 P0174 and a p0171

2008 Silverado 2500 6.0 has a p0171 and a p0174. Intake was smoked with no leaks truck came to me with 8 new injectors a new fuel pump new map and mass air flow sensor and new intake gaskets. It has had all 4 o2 sensors changed twice. The long term fuel trims sits at 24.2 all the time and the short term is anywhere for 10 to 19. The up stream o2 appear to be fluctuating. When you go wot the short terms will fall but there is no effect on the long term. Fuel pressure is at 62psi running and it appears to have had a recent tune up. This has been an ongoing issue for a while now and the dealer has washed their hands of the vehicle. Im the fourth guy to look at it and Im stumped. I was thinking maybe an ignition issue because there is a rough idle and sort of a flat spot when trying to hold the accelerator pedal down. It goes from 800rpm to 2000 and there is no real in between unless your actually driving the truck.

Update!!!

So I decided to try some simple stuff and put a vacuum gauge on it. When you start the engine cold it is slow to build vacuum only like 15" and then gradually increases to 18". When you rev the engine the vacuum goes up to 22" and when the throttle is release it drops clear to 15" again for a second or two and then goes back to 18". Ive always been under the impression that vacuum is supposed to drop with more throttle not go up.

have you checked for a stuck open purge valve?

have you checked fuel quality to make sure its not e85 runnning in there? also maybe try a fuel trim reset with a scanner

The purge valve had been replace but i checked it pulses when its running. This vehicle is not flex fuel. I did smoke the evap line and had a ton of smoke pour out a filter looking device on the passenger side im assuming that its a filter for the valve down by the fuel tank and assumed it was normal.

any misfire data?

what i meant by the e85 was. check the fuel quality make sure there isnt e85 in the tank instead of regular gas.

nope just the lean codes. The is does have a bit of a rough idle and slight miss when you hold the throttle at any given rpm (im thinking thats from running lean) but there have not been any misfires recorded.