My mom has an 88 Astro that started shaking real bad. It shakes whether it is sitting and idling or going down the road and increases with the engine rpm. I thought for sure it was one of the motor mounts because of the way it feels but when i checked, the motor and transmission mounts appear fine. Any one have any idea as to what I might check for next? It feels like it's not balanced right. Do harmonic balancers go bad? That is the only other thing besides the flywheel that would make any sense. Any insight would be greatly appreciated