Wrench Light comes on and Power drops drastically - especially up hills. on 2006 Ford F-350 Super Duty

Just bought this truck used. Only 71k miles. When pulling Trailer, particularly when I have to excellerate up hills, yellow wrench light comes on and I have a significant loss of power. If I pull over, restart, it seems to reset and I'm good until the next time. Please help. Sucks to have this problem my first month of owning it and its been very dangerous - especially with horses long distances.

Don't even know where to find Diagnostics in the area and I know a dealership is going to see me pull in and soak me. I spent all my bucks just to buy this thing.

Asked by for the 2006 Ford F-350 Super Duty
this could be many things - i'd start by changing the fuel filter. if you see no change you just might be forced to take it to the dealer. there are some good independent shops that work on diesels.