The vibrations I experienced due to bad motor mounts disappeared at higher rpms. As indicated above I'd check for drivetrain issues. Also check your fan - bad bearings can cause vibration that increases with rpm.

__________________
Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica