It has come up more and more. Everyone should know whats in the truck. Below are the stock gear codes found in the glove box. You will have one and possibly two of the following codes if you have the G80 option. I have also listed a helpful gear to tire size chart to help people better understand.
GT4 -- AXLE REAR, 3.73 RATIO
GT5 -- AXLE REAR, 4.10 RATIO
GU4 -- AXLE REAR, 3.08 RATIO
GU5 -- AXLE REAR, 3.23 RATIO
GU6 -- AXLE REAR, 3.42 RATIO
G80 -- AXLE REAR, locking differential (has many names, none being good but that brings up a whole other discussion)
GT4 -- AXLE REAR, 3.73 RATIO
GT5 -- AXLE REAR, 4.10 RATIO
GU4 -- AXLE REAR, 3.08 RATIO
GU5 -- AXLE REAR, 3.23 RATIO
GU6 -- AXLE REAR, 3.42 RATIO
G80 -- AXLE REAR, locking differential (has many names, none being good but that brings up a whole other discussion)