Ive got an 02 GT. Recently had the transmission redone under warranty because 4th gear synchro went out. Waited about 2 weeks before i ran the car hard and noticed at about 110 mph the car had a terrible vibration. It felt like a drivetrain vibration instead of tires. To make sure i took it and had the tire balance checked and inspected for any flat spots or possible causes. They were perfect, took it back to the dealer and they inspected it to make sure the driveshaft was aligned properly and it was. The shop foreman there is a wonderful person to deal with so i feel like he is telling me the truth when he says he has NO idea what can cause that. So my question is has anyone ever had this happen or possibly know what it could be? Thanks for your help. I do have 3:73 gears which had been installed about a year ago.