88 rs 2.8 with a 5 speed.... my problem is that no matter what gear i am in,at about at about 2800-3000 rpm,i get major vibration in the motor. the trans is fine and tight, but nothing over about 55 in 5th gear, or it feels like it will break from the mounts,"wich are new" the motor has no problems until it is under load..any help will do.......

 

Have you tried using throttle body cleaner, and really cleaning out the throttle valves and vacuum ports, IAC port? I just did it this week and my vibrations stopped. turn car off first, or do on a cool engine.