I recently purchased a GLS from a very good used car lot - willing to fix anything in the first month. Also with a drivetrain and transmission warranty for 2 years or 30,000 miles. Three times now while highway driving the car started to shake and shudder, really felt it in the steering wheel. Felt like a wheel was out of balance. This happened between 40 and 65 mph. They checked it out - no codes. Thinking the engine might be missing I punched it down - only got worse as speed increased. I let off the gas and while approaching a stop the car didn't seem to roll freely - any ideas.