Have an 06 4WD Dually and the new tires I put on last year a really starting to cup bad. Truck was lined up when tires were put on. Runs down the raod strait with no hands. No shaking of any kind.. I was at a garage the other day and they had a display for Monroe shocks. It showed a picture of what my tires look like and it said it could be due to bad shocks. they are the original shocks that came on the truck (King Rancho) and there is almost 80,000 on it. The display said you should replace the shocks every 50,000 miles.. Im starting to think... What are your thoughts to my problem?