I've been away for a couple of days, sorry for the delayed response.
I would swap tires front to rear and see if that changes the vibration. If it does, take the others advise and check, replace or balance tires.
If not, then you know it isn't tires, engine or clutch (since it doesn't do it reving sitting still).
Then check the u-joint, it is possible that it is not properly seated in the trans yoke since the PO replaced it, or worn due to lack of lubricatiion when it was replaced.
