So I've been trying to fix this issue for about 2 weeks now, and I can't seem to find the solution

The problem: Every morning starts and idles just fine. Hesitation problems around 2000-2500 rpm when cold and progressively gets better as it warms up. Still will hesitate at running temp when cruising down the highway at about 70mph but eventually (5 miles) evens out and everything returns to normal. While cruising down the highway the rpms are about 300revs higher than normal, until it evens out. Doesnt have problems at wide open throttle, nor pretty much anything over 2500rpm. Could go about 10 miles total before it starts acting normal. Park the truck, go to work and come back 8 hours later and it runs fine. No active, nor pending codes.

Attempted fixes: Cleaned EGV, MAF. Replaced tps, coolant temp sensor. Fuel pump was replaced about a month before issue started. No matter which fuel injector cleaning used no improvement, seaform in intake no improvement.

Any suggestions are greatly appreciated.

 

Mine is doing very similar to what yours is doing and has been doing it for a while. I have replaced plugs, plug wires, distributor cap, fuel pressure regulator, thermostat, planum intake gasket and throttle body gasket, charcoal box, and fuel filter. Still does it. I think I have it narrowed down to one of the upstream O2 sensors as the gas milage has dropped also. Will be replacing this tonight or tomorrow and will keep you posted on the outcome. Its a 2000 LS 4X4 with zr2 package and about 170k.