i have a 99 1500 with the 4.8, my truck is not wanting to start like it should , u can crank it sometimes for 5 or six seconds nothing , the turn the key off back on it will start but its idleing really low like its gonna die then it will idle back up fine , but if u dont set and let it warm up for 5 min or so and try to go up the road it will spit and sputter like its not wanting to take fuel,then by the time i hit bout 3rd gear it will clear up. i just replaced plugs , plugs wires , air filter , fuel filter ... any ideas what this could be?

 

Intake manifold gasket? As the intake heats up it may seal things up better and run better, but when it's cold it allows more air to get sucked in, causing you to run lean and be tough to start/idle.

 

Maybe have your fuel pump checked the pumps in these trucks dont last forever and can cause all sorts of odd problems. Most shops should be able to check your fuel pump. if it feels like its not getting the fuel then it probably isnt.

 

its the fuel pump i have a 99 silverado 2500 with the 6.0 and mine around the 250k mile mark did the same thing need to prime it a few times and it would start then when it got really bad it would idle 200 rpm or so and it would be rough and die to fix it i took the bed off and changed the pump which is on top of the gas tank so you have two options drop the tank down or pull the bed sence my truck has a 34gal fuel tank and was almost full i just took the bed off because it was a long bed there was 8 bolt on a short its probably 6 not hard to do at all once i changed the fuel pump everything went back to normal also you can buy just the pump from rock auto 60$ and re use the housing if nothings wrong with it and make sure that that all hoses are on tight or they will come off and you will have to pull the bed again