8-3/4 Noise After Rebuild..What's Normal??

If you're sure it's "gear" noise (which it sounds like), then all the posi lube stuff is just barking up the wrong tree. You'll potentially experience three types of gear noise: Accel, decel, and coast. If it's a high-pitched whining sound you're hearing on both accel and decel going straight down the road that changes frequency in direct proportion to speed which still persists after a a couple hundred miles of break in, then they are definitely not set up right. Probably excessive backlash.

My 3.73 gearset is a cheapie chinese version that has a coast whine to it. It shows good pattern both ways, and runs fine. Sometimes there's gona be a little noise, especialy with the less than quality gears. But yours definitely sounds like a setup problem.