Vibration problem. Feels like your driving over rumble strips on the highway. 35 / 65 mph so far … 55,000 miles
Could be a drive shaft issue. Have you tried going to your dealer?
If the problem starts after you reach 35-40 mph, it is very likely to be a problem with the torque converter lockup mechanism. The good news is that, unless you have racked-up a lot of odometer miles in the two years that you have owned this vehicle, your Powertrain Warranty is still in effect, and it will cover the repairs–in full.
Just take it to the dealership, have a mechanic ride along with you, and demonstrate the problem for him.