Is there a site you can go to for figuring out the option codes in the glovebox? I was curious as to the rear axle ratio in mine. I just bought it and it has the tranny cooler/towing package, the guy said he thought it had 3.73's but I'm just wanting to know for sure.
Thanks,
Matthew

There's a chance this thread might help:

http://67-72chevytrucks.com/vboard/showthread.php?t=186516

for 06

GU5 is a 3.23
GU6 is a 3.42
GT4 is a 3.73
GT5 is a 4.10