Has anyone experienced this or have an idea of what might be the cause? I was just getting up to full speed on the highway and my 01 Discovery went out of control. I slowed down almost to a stop and got it under control, but as soon as i picked up speed it started again...I'm not able to drive it over 40mph without losing control. A guy who was driving behind me when this happened said my front driver tire was wobbling pretty bad. Any help would be greatly appreciated!

 

Sounds like you need to crawl under your truck and see what is loose, make sure to check your lugs nits, tie rod ends, everything. You haven't mentioned what the mileage is but I bet part of your problem is the steering stabilizer. Might also want to check and rebuild your front drive shafts constant velocity joints if they do not have grease fittings.
Mike

 

This could also be a bad tire. If you have severely damaged belts or other carcass damage you may see something like this. Look for deformations in the tire.

 

I would take a look at suspension joints, maybe control arms or tie rods. It really sounds like you have a ball joint that has gone bad. I wouldn't drive it anymore because if it is a steering component it could break completely at any time and you could cause a serious accident. If you can get under or close to the underside take a look at your steering components and if you can give any of them a tug you should be able to tell. Something that bad would be pretty noticeable.