92 Chevy 3500 shakes while driving?

this happened to my brothers jeep. if the truck has the function where it automatically locks in the 4 wheel drive when a tire slips then check your tires all around if one of the tires is larger or smaller (especially on the front end) this will cause a slipe in one of the tires then the truck will try to lock in the 4 wheel drive causing it to shake violently........ this will be easy to check and will be a cheep place to start.........