Have you considered something in the gas tank, such as rust or particles floating around? Or even water in the gas tank? My initial thought would be to check something like this since the problem is so intermittent. I've never had this problem myself, but I have heard of fuel lines getting clogged or partially blocked with things moving around in the tank, causing the vehicle to run fine otherwise. If you turn off the engine, let the truck sit, and start it up again does the problem go away?
If you're not driving the truck too much how often do you fill up the gas tank? It could be possible that you have bad gas in the tank as well.
Just my $0.02... and I'll be curious to know what the problem is too!
~Neil
