I`ve just bought a `96 Colorado 3dr diesel manual which is great except for an annoying vibration through the floor under hard acceleration(especially when labouring the engine in 4th & 5th gears)
Suspected engine/gearbox mounts,but they don`t look too bad.
Anyone got any ideas?

My mate had a similar problem it could be that the bearings in the uj's on the prop shaft are worn or damaged caursing the propshaft to be un ballenced coursing a vibration affect i would advise checking this area first.