noise in rear 93 silverado HELP PLEASE

I have a 93 silverado Z71 with a 4" lift and 33" tires. I was driving down the highway when all of a sudden the whole truck started shaking. A couple of seconds later it got way worse where I had to pull over. I continued to go and it was still shaking but not that bad. It felt like it was coming from the rear end of the truck.....couple people told me it might be my U Joints. anyone else know what this could be? its not the lugs I checked them and they are tight

I'd probably go with U-joints also. Lifts put a little extra stress on the u-joints. Also, check to make sure you didnt throw any wheel weights off. If a lot of weight was needed to balance the tire when it was put on, if it comes off it can make the truck shake like hell.

I agree, it is probably the ujoints. Crawl under your truck and shake the drive line up and down and twist it back and forth watching for play. Do this at both ends watching for play. Watch for play in the u joints as well at the pinion.