When you go in for tires make shure you get E rated tires. I got hosed on a deal with discount tire. They gave me D rated and every time i get over 50 it startes drifting on me. I feel like i'm playing pong going down the road.

 

Get yourself a DSS now that everything is good, it will support your gear box and really straighten up your steering. Had mine on for 3 years now.

 

Even with D's, you shouldn't have a problem if they aren't overloaded... you possibly have a defective/out of round tire.