I'd like to find out what my '95 Z28 (automatic) has for the final gear ratio. I believe it is also referred to as the differential or the rear-end. Is it in an RPO code on the door?

 

In the glove box. It'll be GU2 or GU5.

GU2 : AXLE REAR, 2.73 RATIO

GU4 : AXLE REAR, 3.08 RATIO (V6)

GU5 : AXLE REAR, 3.23 RATIO

GU6 : AXLE REAR, 3.42 RATIO

 

Alright, thanks a bunch. Can you tell me what the differences between them are? I'm assuming the higher the ratio, the higher the RPMs go before the auto shifts gears.

 

Not necessarily. The higher the ratio, the higher the engine will rev at the same forward speed. The computer controls the auto shifts, so it's however the tables are setup as to when it shifts.
Higher ratios give you more torque multiplication. Changing to a higher ratio will make it feel more responsive, but may not be necessarily faster. You have to take the total package of engine, transmission, suspension, etc. into consideration.

 

Okay, I checked, I have GU2. Is this the standard one for automatic Z28s or the optional one?

 

For automatics, GU2 was standard, GU5 optional.