I have a 2003 Chevy 2500hd with the 6.0l starts fine after sitting for a few hours but after shut off for a short period the throttle has to be pressed all the way to the floor to start then runs terrible. I replaced the pressure regulator no change. Yesterday while heading to work the truck out of now where ran perfect then I went to start it after work to head home it would stumble back fire then it would die if I touch the throttle with any pressure. If I put the pedal to the floor and start it would start up rpms would come up then would die like there was no fuel.

New pressure reg
New iridium plugs gaped at 40
New plug wires
New tb

Does not go into limp mode.

 

do you have a fuel pressure gauge? see if the fuel pressure is leaking down

 

Just bought a new tester mine I'll test it tomorrow.