The vibration occurrs around 2500 rpm on the engine -in first gear, in second gear, in third gear, etc. It does not occur at a particular automobile speed which would be driveline related or possibly wheel balance, alignment, etc. It does not occur under light load but under moderate load and higher. It is not present below 2,000 RPM and it does not appear to be present above about 4,000 rpm - in each gear - whatever speed I may be going down the road.