RPO Code Help

[DuckHunter]

I attached a picture of my rpo codes inside my glove box. Now for my questions. GT4 says i have--Rear axle, 3.73 ratio. Is this common ratio my last truck had 4.10 which is better? G80 says i have--Differential, heavy-duty locking rear. Is this common what exzactley does it mean? KNP--Cooling external transmission oil cooler. What exzactley does that mean? It also shows z71 does that mean i have z71 package?

Here is the link to run RPO Codes:
http://api.viglink.com/api/click?fo...//www.tahoeyukonforum.com/forum/showthread.ph p%3Ft%3D5846%26page%3D2&title=How%20can%20I%20find%20out%20what%20rear%20end%2Fgears%2Fdiff%20my%20truck%20is%20equiped%20with%3F%20-%20Chevy%20Tahoe%20Forum%20%7C%20GMC%20Yukon%20Forum%20%7C%20Tahoe%20Z71%20%7C%20Cadillac%20Escalade%20-%20Tahoe%20Yukon%20Forum&txt=http%3A%2F%2Fwww.gm-trucks.com%2Frpo-code-lookup%2F&jsonp=vglnk_jsonp_13278804351393

 

[chauncey0337]

3.73 is common. Some 'upgrade' to 4.10 for better take off(torque) but also results in lower high end speed. Trans cooler, I think, is in front of the radiator. It looks like a small radiator. And Z71 was a chevy option, not gmc. The z71 means something else.