& another potential (I had that once) is not enough front yoke engagement into the trans (& or bad ext housing bushing). Mine was a PT vibration at random sort of (mostly deccel) & I swapped the correct shaft in & all good.
The snout on the front of the driveshaft is better than 3/4 engaged into the tailshaft and the snout is roughly 6" long. Before the 3.91 swap, I didn't feel anything off at the same highway speed. Maybe bc the engine revs were lower.
I have run up to the same speed in 3rd and that is about 3300 rpm. Couldn't really tell if it was there, probably because of the added harshness from the engine. I don't think the motor mounts are the softest.
If the tailshaft bushing in the trans has wear, should I be concerned until I can get the trans out and freshen it?
