Need Help Possible suspension problem
What kind of driveshaft are you using, and how long have you been running it? With a 9" it typically takes a one inch longer shaft. If the shaft is the factory length, it may not be going deep enough into the tail bushing of the transmission which may be causing the extra play. This could create more wear on the bushing and even cause it to pull out of the tailhousing.
The play in the driveshaft is probably the backlash in the rear. If it has a detroit locker in it it will feel like it has an extreme amount of play, but that is just the design of the locker. I'm sure you've checked the u-joints.
I'm not really sure how anyone could hear a strange noise in the trans when turning it by hand. What does it sound like when the engine is running in neutral and the clutch is engaged (pedal out)?
We'd be glad to take a look at it if you feel its in the transmission. Since you're in VA you could just drive or haul it on down here. If we did something wrong on our assembly we'll make it right.

