Last weekend, I hand-checked the drive shaft & noticed that the pinion at the differential could be rotated about 1/4" freely, while truck was parked in gear. Since then, I parked the truck as-is & went back to work in Vancouver.
Yesterday (Friday), my gf used the truck & the noise/vibration continued and got worse. The sound began as soon as she started driving and progressively got worse.
It sounded like a wrench banging on a metal pipe. The more gas she put, the faster & louder it got. As it became worse, it got louder with a stronger vibration.
On the way home, at a yield stop, after she put it in 1st & let off the clutch very gently, the whole truck shook violently upon acceleration.
She clutched in a second time and kept adding gas until the truck got going. Banging noise & shaking continued.
At the next intersection (before calling the tow truck), she experienced the big bang and shaking again, but the truck wouldn't go forward. She tried again & the truck was just revving with the gear engaged. She then gravity backed-up onto half of someone's driveway and reversed the latter half of driveway. No noise/vibration was observed when backing up.
I just traced down (visually) some slipping action at the pinion/driveshaft. I really hope this is just my pinion/rear 3rd causing all these problems & not anything else?
FYI: My current rear 3rd is a 94' V6 Auto 4.88 modified with 87 Supra LSD.