88 Vert Vibrations
 

Hi everyone so I'm new to owning a rotary but not new to working on them, I recently purchased an 88 vert which vibrates from around 4-5k rpm upward whilst driving or in neutral, I've checked the driveshaft u joints and they are okay and the engine and tranny mounts seem fine, what else could it be as I really would love to fix it, thanks guys :)

You said you checked the motor mounts already but that's what I would think it would be. Maybe they are poly mounts?