To start with my truck is stock as far as I know. I bought it used with 59,000 miles on it in January. It now has about 79,000 miles. I was noticing what seemed to me to be a loss of power when the RPM's would pick up when I would get heavy on the throttle. About two weeks ago i was pulling my travel trailer (about 9,000 lbs) and towards the end of the trip it seemed to get a lot worse. I was barely making it up any hill what so ever. If the truck needed to down shift and the RPM's went up I was losing all kinds of power. So I figured fuel filter, right? Well I changed the fuel filter located up in the engine compartment at my campsite and seemed to be running great. Better than when I first bought it. So I thought my problems were solved... However on my return trip, nearly 700 miles into it, the problem returned. I'm kind of at a loss. It seems to me that there is a fuel delivery problem somewhere. That fuel filter could be plugged already, could it? Are there more than one fuel filter normally? Guys any help would be appreciated. This is my first duramax, diesel period for that matter, and I'm starting to get frustrated.