It's not the shocks and you don't need a steering stabilizer.
Do a search and you will find an ENORMOUS amount of info on this subject... more than likely something is loose in the front of your rig... wheel bearings, ball joints, control arm bushings, tie rod ends, track bar. You need to go over everything with a fine tooth comb.
Throwing money at it by doing stuff like buying new shocks or putting a new steering stabilizer on will either A) be a waste of money (shocks) or B) put a band-aid on it until things wear out enough to over come it (steering stabilizer).
Don't bandaid your front suspension... if something is loose FIX IT because you're endangering your life AND everyone elses life.
BTW, for an interesting fact... Out of balance tires can set death wobble into motion at higher speeds, but if the truck is otherwise normal until you hit a bump, then it's probably not tire balance. I run 36" bias ply Iroks with NO balance weights and drive it 70mph down the freeway and not a hint of wobble when hitting bumps, bridge transitions, etc... but if I get going fast enough, it can start to feel a little wierd.
