I have no mechanical expertise but I do like trucks. So I have a 2008 Suburban LT3 with approx. 80K miles. For the past year, the truck will occasionally hesitate / sputter / rough during a warm start, never during a cold start but runs totally fine afterwards I don't drive it much, live in the city, 1-2 times a week, short trips. By occasionally it may happen once or twice over the span of several months. Most recently it occurred last week, I drove for about an hour, stopped for 15-20 min and it happened but it does start without repeating the another crank. Later that same day I stopped to get gas and it did it again. This time I tapped the gas pedal and it shut down. The next crank it did not start but did on the next and ran fine for the 1 hr drive home. In the driveway I stopped/started several times and it never repeated. Neither I or my mechanic can ever replicate the issue when we want to. Within the last 12 months the mechanic has replaced the battery, starter, temp sensor, evap vent, gas cap ( check engine light was on) but the mechanic ( a family friend) without being able to replicate the issue says he just does not know fir sure what it could be. Given its age I am reluctant to just start replacing parts if he is not more 50% confident. It has been so long I figured whatever it was would have completely failed and left me stranded by now, but it has not. I even took it in on a couple 8 hr road trips last summer . Any ideas what it might be?

 

Basics first. How old are the plugs and wires? How does the air filter look? You did not give engine size, 2 available-a 5.3 and a 6.0. Likely makes no difference but complete info works best. I would recommend going to the parts store and get MAF/MAP sensor cleaning kit and follow directions to the letter. I would also recommend cleaning the throttle body. Your friend likely knows how to do all this.

 

Possible seeping/sticking injector, semi floods motor on those 15 min. stops. Give it partial throttle when it acts up and see if it starts easier. Couple tanks of gas with a good injector cleaner will not hurt especially if you use no name gas all the time. Use Techron or one with PEA in it.
Cold motor likes extra gas, hot motor will be hart starting and chugging until extra fuel clears out.
I toss a bottle of injector cleaner in the gas tank at every oil change in all my vehicles.