when on the hwy car starts to vibrate after 72mph. seems to come from the rear, also i found that the sway bar bushing mount on the pass side was broken so after replacing not as bad but still there, everything else seems to be in fair condition. tires are balanced. the vibration is not affected by on/off accelerator, tranny mount is good. any one else had problems like this??

ok so if you feel it in the seat it is in the rear, if it is in the drivers floor it is the front. so at 70+ you are on the outside of most balancing machines, are you 100% they got the balanced to 0 weight needed. and how much weight do you have on each side. it could very well still be a tire balance issue. Could be a drive shaft balance also but not to likely.

if there is alot of weight on one side of the wheel have the tire shop break the bead and rotate the tire on the rim and try agagin it should be less weight. less weight is ledd chance for vibration.

You could depending one your wheel and tire size. rotate fron to rear and see if the vibration moved to the front. if not then it is something other than tires.

I am a tire/oil changer so I balance alot especially my own. On my daily driver i have bent rim and i can balance it and it still shakes at high speeds, When you get the balance check to see if your wheels spin true.