RPO Codes: One oddball in my list

This question may be posted somewhere around, but I didn't see it in my searches:
A few days ago I was watching a video linked from here regarding the G80 RPO Code indicating the Eaton Locking Rear Differential. I got curious and started looking up all my RPO Codes for fun. I've got a 2007 Silverado 1500. All my RPO codes seemed right / fine with the exception of "1LT". I have no idea what this one is, and I've only seen it noted on Malibu codes as the LT-I trim package. I've checked the sticker, it's not a wrong note on my end that I can see. I still have the original window sticker, and it's an LT-II Package on there.

Anyone have any ideas on the "1LT" RPO Code? If not, it's no big deal, I was just wanting a complete list for fun.

I'm using these two sites for my lookups:
http://www.gm-trucks.com/rpo-code-lookup/?find=1lt
http://www.c2e.info/rpocodes/gmrpocodes0through4.html

Thanks all!