I have an '08 6.7 2500 all stock with stock wheels and tires, while driving at normal speed , if I turn steering wheel slightly left then right the truck feels "wishy washy " like the front end goes right while the back end goes left. any ideas ?

 

Sounds like low tires.

 

If you don't have many miles on your truck this is completely normal. It's the tires. When I had a new set of tires put on my truck I got this same senario. It takes 2,000-3,000 miles for the sealer to scrub off the tires. Until then, it's miserable.

Edited: Oh, and you can spin the crap out of the rears if your not careful...LOL