Not sure what it could be, but whenever my fuelpump went out I was getting on a freeway ramp and the truck felt weighted down, I had the pedal to the floor and it was just spitting and sputtering, I finally made it home and noticed how loud the fuel pump had gotten. I think at the time it was like $475 for a new fuel pump assembly. But thats the simptoms I had, good luck on getting your truck back in order.