seeking expertise on intermittent burb vibration

We have a 2003, maybe 2004, burb that when in 4 wheel auto, on occusion, has a terribale vibration when steering, usually to the left. The vibration can be stopped by switching to 2 wheel and then back to 4 wheel auto. The dealer is resistant to say thier is a problem. But the car didn't do this when we bought it new (15K miles go) and the new ones on the lot don't do this in comparsion drives and our 96 Jeep never acted this way.

Also, why would the dealer say to keep the car out of 4 wheel auto? They claim it should be in 2 wheel most the time. We got 4 wheel drive mostly because of kids, colorado, and skiing but we like to leave it in 4 wheel auto for quick road condition changes. Educate us!

Any help or suggestions would be appreicated.
kswerner

make sure your tires are all the same if they are different size or tire pressure front to back this can happen. don't let the dealer get away with this. if new one don't do it it's not normal