vibration 60mph and up

I have significant vibration from 60mph and up. I have changed the bushings, shocks, had an alignment, and put on new tires. Vibration is still there. When I pull my boat, there is less vibration. What should I consider doing next?

Check the U joints. If you have 4X4 and think it may the front U joints, you can isolate by removing the rear shaft and then put into 4X4 mode and drive the vehicle. If you still have vibration, the the problem is in the front. If no vibration then it's the rear U joints. Post your results.