I recently installed a polyurethane transmission mount to replace a very worn factory mount. At idle and around town it feels fine, maybe a little more vibration, but nothing too drastic. On the freeway it's a different story. Everything's fine until I hit 60, when I start getting big time shaking and vibration. I can feel the steering wheel shake in my hands. It used to run fine up to 75-80. I was planning on switching to a stock-type rubber mount to see if that fixed it, but when I described the problem to a (non-Ford) mechanic friend, he thought that it might that my u-joints were going bad, and the worn transmission mount had been masking the problem. Any opinions or thoughts from the forum? I'm sure a new set of u-joints couldn't hurt, but I don't want this to turn into one of those situations where I replace part after part trying to track down a problem...