GMC Repair: Safari runs 1-2 seconds then stalls, distributer cap, gmc safari

Question
I have a 99 GMC Safari van, 4.3 litre engine. Sometime in order to get it to start I have to put the gas on a little. If I forget sometimes it will start but mostly it will turn over, start and run for about 1-2 seconds then quit. It will not start again until it sits for a while. Some times 10 mins, sometimes it takes an hour. No rhyme or reason to the time. It does it in all weather types, when the engine is hot from running or cold. We've had a tune up, the distributer cap and wires replaced. Our dealer has hooked it up to all the computers and says it is running just fine. Any help with this problem would be greatly appreciated.

Answer
Hi
I would get the fuel pressure checked. These engines need 60-66 PSI to start. If not they WILL not start or be hard to start.
If fuel pressure OK I would have it properly diagnosed at a shop your familiar with.
Have them check fuel pressure.
Have them check for spark while cranking.
Compression.
These are just suggestions.
Good Luck
Just advise from experience.
Pawl