Hi, I was wondering if someone could point me towards some information about what type of rear end this is. It's in my family's 1998 Chevy K2500 work truck. I looked through the RPO codes and it has 3.73 gears, but I wanted to find some more in depth information because I'm curious about it and will soon change the gear lube. After a couple hours of searching I'm still not sure exactly what it is. All I know is that it's a 14 bolt. The only marking I've been able to find is 646. Is there a way to determine the ring gear size? Whether it's full or semi floating? Which cover gasket will I need once I change the oil? And then which oil should I use? Dino or synthetic, then with or without lubricant additive?