Suspension
If you can't see anything physically bent/cracked/broken then I would take it to a body shop and have them put it on a frame machine and they can tell you what's wrong.
My car was wrecked before I bought it. The k-member and frame were bent bad. I took the car and another stock k-member to the body shop and they straightened it for $250. My motor was out of my car though which will play some effect in the pricing.



