this truck has the x-tended cab and is 4 wheel drive. It began making noise and vibrating at high speed the other day…like when driving on the out-of-bounds drunk bumps. I found that when I engaged the 4-wheel drive transfer case, with the hubs unlocked, the noise went away for a brief period, but then would start again…especially after hitting a bump in the road. The noise & vibration will happen at any speed. It was suggested it might be the carrier bearing, but I checked that (pulled the drive-line) and it is tight. I had to back out a trailer in 4-wheel drive the other day and the phenomenon went away for several days, but is back now. With the windows down I can hear a clacking sound (not a clicking sound) that goes along with the vibration.
Worn universal joints on the drive shaft maybe?