I just bought an '05 Yukon XL. 2500, 6.0 w/ a full towing package. I'm thinking it's got a 4L80E, but what code should I look for on the data sticker? Also, what code should I be looking for w/ the rear end gearing? I did find that it's either a 3.73 or 4.10. This thing spins at 2,000 RPM at 60 mph...

 

should have the 80E..
M30 is the 4L60E i know that much for sure.


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, LIMITED SLIP (POSITRACTION)

 

I just took a look. It's got the 4.10 (GT5).