What goes up usually comes down. New diff mounts actually have a little bump of rubber in between the metal pieces to absorb the shock,
The stuff after "Since" doesn't quite make sense.
"Since" meaning, once the problem started I have put on new diff mount, half shafts, and new drive shaft.
A substantial piece of the diff mount has been grinded out by the flanges of the half shaft. During downshifts and reverse only. I can floor the car with no problem.
All bolts are solid, so I think. What could be allowing this...? Could the diff itself be screwed up...?