I need to get my girlfriends 98. 5 3500 in the shop to get looked at. It seems to be losing power when pulling the horse trailer. We have taken the truck to Desert Diesel in Tucson a couple of time but just don’t get a warm fuzzy about the quality of the work. The truck will be running along fine and then just lose power under load. Drop the truck back to 4th or even third and eventually the RPMs will pick up and it will take off again. I know the truck has had a lift pump and a VP replaced before. The truck has not done this while I have been driving so I can’t get a better description of the problem.