I have michelin ltx at tires on and we took the truck to dodge because at high speeds it vibrates really bad and they said the tires were really cupped. It looks like the outside of the front tires are really worn but the inside is hardly worn. The tires have 75,000 miles on them. Is the uneven wear a result of misalignment, not rotating them enough or could it be from a bad ball joint?

 

Tires should be rotated regularly for maximum wear. That being said you still probably have a worn part or alignment problem.

 

You have 75,000 miles on your tires and you are asking about wear? I would say that you have gotten your $'s worth out of that set.
I think 5K or so is good mileage for rotation. I usually swap mine around every other oil change (about 10K). Michelin is a GREAT tire, my wifes Stratus went 91,000 on the OEM Michelins. (she had a blow out in one of Baltimores fine neighborhoods) I have 67K on two of my OEM's, they are SHOT, waiting till fall to get 4 new ones.(unless I find an '05 take off set sooner)

 

75K!!!! Wow! In my experience with the 4X4 trucks you will always get a little more outside edge wear on the front tires.

 

If the tires are cupping, you're balljoint(s) are probably shot. Jack up one side under the axle, then use a piece of pipe and pry underneath the tire in a straight up and down motion, then try and wiggle it side to side. Watch for play in the balljoints. When I worked at Tires Plus, 95% of solid axle trucks with cupped tires had bad ball joints.

 

On our dodges, the front ball joints have a little play up and down. Check for in and out play. jack it up and pull out on the bottom, and push in on the top, and vise versa. if you have play in and out on the top and bottom, then you know you have a bad ball joint.

I check some brand new trucks with the jack it up and use the pipe technique, and they moved some also..

 

Have you checked the shocks, most alignment shops I've been in have a wall poster. Usually the first problem/description is cupping and the cause is shocks.

I'm an expert at wearing out steers, two sets in two months. Bout replaced everything under the front. . .then the right rear duallies fell off. . .again.

Cheers,
Steve J