I have an 03 Lariat with about 14,000 miles. About 3 weeks ago, I started the truck and put it into reverse. Even before I let off the brake I could feel a shaking sensation. It continued to shake and I backed up. Then seemed to continue as I drove forward slowly. Eventually, I noticed it less as I accelerated. Since then, I have not noticed this when standing still, but I have sensed this shaking a couple of times when doing about 30 mph. Has any one heard of anything like this? So far it has not occurred enough to try and get a handle on it.