My 1990 Chevy trucks steering wheel just started vibrating and moving and my truck keeps on bouncing at low speeds what could be causing this?

possible front tire seperation. If you've recently been off-road, check for mud/snow/ice/whatever stuck in the wheels. I had an '88 Chevy with offset rims, and when you got mud stuck in them, the truck bounced around so bad it felt like the wheels were going to fall off.