problems your trackbar.
replace it. you're experiencing deathwobble most likely.
the reason you dont' feel it all the time is because it takes a certain bump at the right time to set it loose. that why you slow down once and it seems ok. afterthat. the longer you drive it like this, the guess is it will get looser, and you'll experience it more frequently.

if it was balljoints or something else you'd feel it all the time.

theres an easy way to find out; get someone in the cab of the truck to wiggle the steering wheel back and forth. watch the trackbar ends for play; there should be NONE. then watch balljoints, etc. nothing should be moving......

 

This is where you've got to start looking for wear. I am surprised that you say your steering is sloppy but everything checks out. Could be the play in the steering box is causing the wobble.

Get a buddy to sit in the seat and turn the wheel back and forth while you lay underneath and look at each component for movement. The trackbar movement will range from slight to slightly greater. Same with the steering gear, tie rods, etc.

 

This is the correct way to adjust the gear box, http://dodgeram.org/tech/mods/steeri...ear/Adjust.htm

 

I am with JonnyZJ, bad track bar equals death wobble.