I can only tell you what I know for sure. I had this exact same problem last year and after having my truck for 3 days the dealer didn't have a clue. They called in tech assistance from GM and it found the FPRV faulty. They replaced it and I was good for a year. Now I have the same problem and I told them that the symtoms are the same. After 4 days they now believe that the FPRV is again at fault. They replaced it and put the truck on a dyno and it failed again so I am still without a truck.
The dealer techs take whatever GM feeds them as gospel. They can change the oil and rotate the tires on Grandma's Caddy, but when it comes to trouble shooting a little diesel pick-up, they are clueless. I should have taken it to a GMC dealer that does nothing but commercial trucks, those guys probably know whats going on.
There are quite a few highly knowedgable folks on this forum and after 2 days with the search button I now feel that I know at least as much about the fuel and control system on my truck as any tech at the dealer that has my truck.
In hindsight, the first reply to this thread is the most valuable, DON'T take it to the dealer. I only have 40,000 miles left on the joke of a 100,000 mile warranty on the diesel engine in light trucks. The only thing that's ever going to get me back to A dealer (definately not this dealer) is a catatrophic failure like a rod through the block.
I'm sorry that I can't be of more help to you but if you have the time, the search button and a few hours reading will make much more difficult for the dealer to pull the wool over your eyes. Good luck with your problem and the dealer, I hope you get it worked out.
Mac on the Jersey Cape
2005 GMC 2500 HD
Crew cab short box 4X4
Air lift bags W/compressor
MBRP SS turbo back, modified MP, pluged turbo resonator