2000 Honda Civic EX Coupe: I have had a new motor recently put in my car?

However it seems that when I go certain speeds on the highway (60-70) my car vibrates. Once I pass this speed (75) then it stops vibrating as long as I drive at 75 mph. Does this mean I need a timing/alternator belt? Or due I need a tune up. I'm due my 200k service in about 6,000 miles.

Have the wheels balanced, I had a car that did the same thing. At 65-70mph it would vibrate badly but when you got up to 75 it would stop. Check the wheels and see if any of the wheel weights have fallen off.

It sounds more like a front wheel balance problem than a mechanical issue. Perhaps a wheel weight was knocked off when they pulled the wheels to change the motor.

What they said, balancing, holy cripes.

Thank you all! I hope that's it because it would be easy to fix and inexpensive!