Looking for advice on a diagnosis from my dealer that my transmission is defective. The vehicle will noticeably shake or vibrate at 80-85 km/h (50-55 mph). I didn't notice this until I installed after market rims with new Michelin x-ice snow tires in November. I took it in to have the wheels checked for balance and was told they were fine. I haven't noticed any other symptoms other than it takes 3-4 seconds to shift into reverse when its cold, This is nothing new as its been this way since new. The dealer is telling me 100% the transmission is shot. Looking for advice or other with experience with this. Does this make sense?