Hesitation

[Rbohno]

I get a bad bog or hesitation upon starting off after my truck has sitting for approximately an hour after it has been warmed up. If I gas it , it will backfire , if I let off and then gas it again it runs fine. It will only do it 3 or 4 times a week and it doesnt last long enough to trigger a code.
Does anyone have any ideas? My brother is a mechanic at one of the local G.M. Dealerships and said maybe an injector was bleeding down.???
Any Ideas ???
Rich