[thstone]

Some thoughts:

(1) My experience with used tires is that they wear very quickly. Not in three weeks, but they do seem to wear out awful fast.

(2) Has anyone checked the 19" wheels? Out of true?

(3) Borrow a set of 17's with stock size tires from a friend, local mechanic, or a forum member near you. Is the rear end still loose?

(4) Mechanically could be bent suspension, wheel hub, etc. Have another mechanic or **gasp** the dealer look at the mechanical bits.

Let us know if you learn anything further.