I'm going to have to agree. Make sure mechanical issues are solved.
Check brakes.
Replace shocks.
Check for worn and tired springs.
Mechanical check goes for front and rear.
Worn springs or shocks in the front will cause your truck to dive even more lifting weight from rear and causing you to loose the essential coeffecient of friction with the road and rear tires.
If you have a disc/drum combo you might want to check for faulty proportion valve.
If none of that helps then you can always wedge two railroad rails between the rear frame rails.
--matt
