Wrench Light comes on and Power drops drastically - especially up hills.

What is your question?

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.