I had a very similar vibration at the same speeds. Is it accompanied by an audiable noise which increases and decreases in frequency with speed? When stopping, does it sometimes feel like there is a damaged or warped rotor and stopping is slightly jerky? When backing up is it smooth or does it feel like it is surging? Does it go away when accelerating through 40-65 mph and come back when you take your foot off the gas for 3-5 seconds? If you have the ability, can you leave your car run in HV mode and lift all 4 tires off the ground and put it in gear and notice the back wheels moving faster and slower? These are all symptoms I had when my PTU went. I also replaced my U-Joints and thought that it might be the problem but it wasn't. I did feel things running smoother, but like you said, it was still there. If you search the forum for PTU failures, I posted some information on it recently because of my PTU failure and replacement.