ARGH! One step forward, two steps back... So I've rotated my tires and changed out my old transmission mounts. Now I've got a nice vibration at 25-30mpg. I reseated my rear tires but have to do the front again just to be sure. I'm thinking it's the driveshaft though. I have new U-joints for all of the shafts, which I'm hoping will fix ithe issue. My existing U-joints are circa 1991 and sound like marbles in can when they don't sound like crushing glass.