I had new frpp 3.73 gears installed in my '07 Gt and now at 60 mph I can feel A slight vibration or more like a low pitch hum thru the floorboard. You can't feel or hear it until 60 and it goes away at 67 or so. Any suggestions?

 

I haven't heard anything about getting a vibration, but the hum sounds like it could be in the "set-up" of the gears..

JMO, but you should take it back to where-ever you had them installed and have it looked at as soon as you can.