96 LE vibration

Take the problem to a real chassis / tire shop. Pep Boys is not the sort of place I would trust to track down a speed problem.

Ed I have same sort of problem after tire rotation. People here advised to check balance

Strut cannot replace alone. They should replaced in pair. I have replaced front upper struts , it coasted me 320 and you will have to do alignment. If problem with struts you will fill it in every decent :) pit you drive over one road. Car sounds like somebody hammers it. Shock works not smooth at all.

I agree with Philip, do not go to PepBoys.

A strut is worth about $70-80 for the part and an hour worth of labor tops... I think it will not solve your problem, most likely a balance issue and/or check your brakes in the rear.

Have someone else drive your car at about 40 mph. Follow in another car and see if any of the wheels are bouncing up and down about once a second. Alternatively, watch it when it hits a big pothole or hump in the road and see if your car rises and falls more than twice.

Pepboys told me today that I need a new strut. Since they didn't really take time to investigate the problem, I am not sure if this is the problem. They gave me an estimate $675. Does this sound about right? Should I take it to another mechanic for second opinion?