I've been asking many gear questions as some of you may know, wondering if 4.56's were the way to go. Today I finally took the time to read my RPO codes in the glove box and came up with these two: GT5= 4.10 ratio and G80= axle positraction, limited slip. I just saved myself A LOT of money. I assumed from reading through the forum that most Silverados, even the 2500HD, came stock with 3.73s but I had a feeling the truck came with posi because of the burnout marks. Also, I never really noticed the sluggish feeling in the truck that some people felt after putting on bigger tires so I wasn't sure if I was oblivious or had different gears. So make sure you check out the RPO codes before you buy anything. No reason to make a few thousand dollar mistake.