Which end is "bump steering" - the front or the back? I'm finding that empty, the back tends to bounce around a bit on bumpy turns.

High inflation pressures tend to increase this, but of course you don't want to underinflate your tires as a remedy. If you have LT tires, you may want to adjust inflation to the load you are carrying - hight loads = increased air pressure and an empty truck = lower pressures. Generally, you don't want to be below the pressure marked in the door for factory/stock tires, and you don't want to be above the max pressure listed on the side of the tire.