I have a 2003 GMC Sierra with the 4.8 engine and auto tranny. I've been experiencing an unusual problem for some time now and so far everyone hasn't a clue.

Basically, if I drive the truck for say 20-30 minutes straight, then park it for about an hour or two, it will stall out when I go to crank it up. I can crank it again the second time and it will usually start up and bog for a second then it's fine. Sometimes it takes the third time to get it to start. Once it's started it runs like a champ. It'll only do this in these exact conditions however.

Several people have said they experienced this same condition and after replacing the fuel pressure regulator the problem went away. I've replaced mine twice now and am still experiencing the problem. The fuel pump does not whine and I have had this problem for several months now so I doubt it's the pump. One guy in the chat room suggested it could be the fuel relay or Crankshaft Position Sensor. Any ideas would be GREATLY appreciated! Thanks.