Hey folks. I'm fairly new to the COM tranny in my '66 F100. The transmission was rebuilt before I bought the truck. While idleing in park; I can feel a vibration through the floorboards right over the tranny. If I put it in gear; the noise/vibration gets quieter. The other day I crawled underneath the truck while it was running in park. I felt the tranny and could feel the vibes.It feels as if something is out of balance. When I take odd slowly down the street I can feel/hear the vibes worsen just before a shift. I haven't pulled the flywheel inspection cover yet but the engine is newly rebuilt. Driveshaft is also rebuilt and balanced. Any ideas?