Just wanted to get some imput. My stock 5.0 is vibrating pretty badly around 4k rpm. I don't think its the balancer as the vibration really doesn't get bad until 4k and seems to get better after or at least doesn't get worse. It feels like a bearing vibration, i.e. too much clearance, but the thing has good oil pressure. Is it possible that the balancer has just slipped slightly causing this problem.