No offense to all the posters out there, but that is a key that attaches to your jack rod, then you stick it in the hole by the rear license plate. It should match up with the screw to get your spare tire down. I had one on my '03, but the damn thing was full of dirt (maybe from some mudding...) couldn't get it down and had to cut the cable.

 

No offense to you but this IS a wheel key.
Plus he has a 2010 not an 03. Same type of wheel key my sister has for her Yukon Denali lugs.

I have a 2010 you don't need a "special tool for the jack rod".

 

I never thought the socket was included with the 2010. Otherwise why would it be so rusty? I'm sure it came with an older truck and got moved to the newer truck because the guy never knew what it was for. These came with the earlier era of trucks for that specific purpose. I'm not saying that it's not the same as a lug key, just more specifically, it is for the spare tire on a pre-`04 truck, they all came with one from the factory...

 

Or maybe, just maybe it is a lug key for a set of older lugs he had on an older truck. I will give you that.

But I've had a number of different types of vehicles and none of them ever needed a "wheel lug" type key to lower a tire. Usually you use the key that the vehicle used to turn the ignition over.