I get a shake around 65 mph, it clears up around 70, it seems to be in the seat which makes me think its in the rear. I just had new tires put on and the tires balanced. I checked the ujoints but they seem to be good and snug. This is a 94 Toyota pickup. Any ideas what to check or is it possible that the ujoints could be bad??

 

Well I have had this problem, and it was my U-JOINTS. The drive shaft had no play in it untill I got the rig off the ground. In the frount the shaft also push up and down a little to see if it moves. I had mine replaced, and the rig ran as smooth as silk. I would say to get the rig off of the ground, and check for play in all directions.

 

Play and wear aren't the only things that can be bad with a U-Joint. The joint should move FREELY in every direction. If it has any "catches" or stiff spots it is bad. The only way to check for this is to remove the shaft and check by hand.

Sometimes when a vehicle is raised by the frame with the suspension hanging, it can pull the joints at a sharper angle and make it a lot harder to tell about play.

 

I'll agree with it probably being u-joints... about only accurate test is to completely remove the drive shafts and check them for moving freely like rezrunner posted