Vibration at highway speeds can come from tire imbalance, tire damage, wheel problems, or drivetrain components. A driveshaft, worn joint, or support bearing may be involved, but the speed at which the vibration appears is only one clue.
Whether you feel it mainly in the steering wheel, seat, or floor can help guide diagnosis. Also mention whether acceleration, coasting, or recent tire or drivetrain work changes the symptom.
Arrange an inspection with Certified Transmission in Council Bluffs, IA. Avoid repeatedly driving at the problem speed to test a severe vibration.