Gears & Axles - Rear Gear Question

I was thinking of upgrading my rear gear. But I have ( 2 ) questions.
1. Does anyone know whew I can look on my car to see exactly what the car was originally supplied with? Will the Vin # tell anything?

2. My car is a mostly stock 99 Z with A4. Longtube & ORY. Would I be better of spending my money on other mods first?

Thanks

Check the glove box for the option codes. GU2 = 2.73's, GU5 = 3.23's (auto cars). GU6 = 3.42's (M6 cars)

Get a stall converter instead of gears, MUCH better bang for the buck.

Actually the RPO code list will be found on the drivers door on his 99.

Ok guys, i just checked the info on the drivers door. GU5 so i guess that would be 3:23. Not what i was hoping for but I guess it could be worse. At least it is not the higher ratio.

Don't forget the "G80" for posi rear. I have been told all v8 cars had the posi, but we are talking about GM here. Never hurts to check. Gears will give you a better seat of the pants feel than the convertor IMO. Do both together for even better performance. I wouldn't go over 3.73 either.