New tires certainly wouldn't hurt. Your bouncing and shaking is most likely caused by and "impact bubble" or a belt separation on one or more of the tires. Bald tires, result in MAJOR safety issues, including traction, steering, handleing, stopping, and if a blow out occurs, you will be throwing rubber and steel shrapnel into everyone else's path that's behind or beside you. Get those tires replaced!
A common problem with the Montana is the power steering pump.
You won't want to. If you disconnect it, your steering will be almost too hard to turn in normal driving.
Check your power steering fluid level.
Rapidly, almost continuously.
Many mechanical and electrical items could be the cause. Even a flat, or almost flat, tire can cause a problem. Check the steering fluid as well.
it is very dangerous to drive with a power steering leak. This is because steering can become almost impossible and you could have an accident.
rad. cap
Sharks never stop swimming. Ever. And they eat almost continuously.
I'm almost positive that the problem is a left or right wheel bearing. Replace BOTH. Easy and inexpensive.
sounds like a bad power-steering line
I had the same problem with my olds, when I took it to the mechanic, he replaced my o-rings and gaskets and cleaned the base, and it fixed the problem, it only cost like 150$ from my mechanic so it might be your best bet to have someone look at it...
One of your front tires is not round.