If that's the case, even sand bags won't help.

If that's the case, even sand bags won't help. unless you put a lot of them :)

The gross weight of full-size pickup is 5000-7000 pounds. a few sand bags won't change a lot in weight distribution.

I think the following can help a little bit:

1. get a crewmax cab, which is large and it will move the center of the weight to the back.
2. install a cab cap on top of the cab.