Truck hops when pulling a heavy load

[greg0380]

Thought I would try posting here, I've got an 85 1/2 ton lwb, 305, SM465, 10 bolt 2:37 gears. I was pulling the boat home (probably 6800 lbs with trailer), and every time I tried to move from a stop, the whole truck would hop around until I got moving. I was talking to a guy at the boat ramp who noticed it and said something about the rear end. I was wondering if there is something I could do to help this.