nasty vibration at speeds over 70

Check and make sure your tires are properly balanced. You may have wheel weights on the rims but they could have moved to a wrong spot and would cause that kind of vibration. You dont want to check U-jouints and such and have somthing replaced when it could have been your wheels and tires the whole time. Check the easy stuff 1st and then the not so easy stuff after. good luck

My car does the exact same thing. I have an aluminum d/s already . I'm thinking it might be something in the rear axle because there is a whine comming from it. Hopefully its not the tranny! Anymore suggestions?

My tranny wines somtimes and has some noises here and there, I dont usualy worry about it unless its super loud or has clunking or odd noises coming from it, Your rear diff may have old fluid in it. You can replace that and I think you have to add an additive from ford or another sorce like bg or lucas oil. Tires in general can also cause a vibration, tires aint perfectly circular and can cause a vibration or a pull. especialy if they are off balance-even whith wheel weights on it. Rims may be slightly bent but its hard to tell on the car. I usualy slap a rim with out the tire on a wheel balancer and just look at it, some rimes are fine and some you can tell the owners smacked them hard on a pothole or curb.

Im gonna do my u joints tomorrow to rule that out , im sure its not a bad idea anyway. Are they a real pain?