What differential in my 96 Collectors edition 6 speed?
 

I have a 96 C4 Collectors Edition Coupe, LT4 with the ZF6 Transmission. Can anyone tell me what the Differential is or how I can find out? The SPI codes on the tag give a GM3 code, which I think is a 3:45 gear, but I don't know the differential ID. Dana 36 or what? Help is appreciated, Think I'm gonna have to remove it and install new pinion bearings. Anyone ever done that?

If stock still, it's a D44 and is a 3.45. Your '96 pinion uses a 'crush-collar' for pre-load vs shims.

This is correct. How many miles are on your car? The D44 behind a stock LT4 should be all but indestructible. Very rare to see someone report a problem. Are you stock? What makes you think you need new bearings?

I'm getting a whine in the rear end when I accelerate, noticeable mostly above 45-50 mph. 52,000+ miles on the car. No noise upon deceleration.

And I have recently changed the fluid, using the proper lubricant, plus the anti slip additive.