My T-6 has 83,000 miles on it and is starting to vibrate in 3rd and 4th gear when accelerating. I don't think its the tires because when I let off the accelerator the vibrations stop at the the same speeds. A new transmission was put in at 72,000 miles and my service person assured me that software downloads were done but I never know with those guys. I think its in the drivetrain and not the suspension. I took it to and indepentent shop for rotors and they looked it over briefly and then I took it to a dealer for torque arm bushing and ask then to check the transmission, niether found any thing obviously bad. I plan on going back to both and have them ride with me. I'm hoping its as simple as a software fix but I'm expecting the worst. Any suggestions or ideas?