Almost all the time when vehicles have vibrations at the speeds you indicated, the problem is in the tires. The belts within the tires can shift and move, causing the tire balance to change as well as making the tire out of round or changing the road force variation of the tires. If an axle or driveshaft were to cause the vibration, it would either have to be bent or damaged. If you have not had a collision and do not hear any noise from the axle joints, it will not likely be from the axles. My suggestion is to check steering components like the tie rods. Outer tie rods have worn out on these vehicles at fairly low mileage and can cause a vibration from the play allowed in the steering. If the tie rods and hubs are tight, have the tires checked for out of round and road force variation. Most tire shops have a specialized balancer for checking this.