Okay so I was driving down the highway about 75 the other day and I let of the gas a little and then went to press on it again and got this really bad vibration. When I layed into the pedal it went away. Around 3000 rpm's is when the vibration seems to be the worst, but only when I'm at highway speed. Just recently it did it at a lower speed today, but usually its on the highway when I'm around 70 mph and 3000 rpm. My first thought was bad u joints on the driveshaft, any suggestions?