75mph vibration

I will take the car back to the shop once I have the tranny back in (currently out for flex plate inspection). I suppose while I have the car on the jacks I can test it to rule out any front end noises. I have run the engine up and down the RPM range in both park and neutral and it's stable as it can be. I have a tach in the car, and when the car is vibrating like hell the tach is still reading rock solid at 1900-2000 rpms. I wondered if anything in or on the motor could be causing this, but I don't have reason to suspect the motor because this just started after the tires were installed and because the car only has 33,000 miles on it.

The tires I had put on the car were Cooper cobras, so I would hope they'd be quality pieces! I will check for the dots when I get home tonight.