Last few weeks I have been getting some vibration while driving at highway speeds (50mph and above). Showed the car to a local shop and the guy said that the rear tires were in real bad shape. Even though the treads were looking good, he said that the tire surface was uneven & bumpy. Could have been caused from bad struts or a lot of "dirt-road" driving that made the surface wear off unevenly (he said he could feel the bumps with his bare hands). He recommended changing the struts and getting a pair of new tires. I mostly do highway driving to and back from work - not sure what might cause this. (It's a 95 Galant with 75k miles). Any ideas? Thanks.