Where's the thermostat??

Truck:  2002 ZR2

Hey guys, I think I got a bad thermostat starting to officially call it quits.  At least, that's what i hope it is.  So i'm going to replace the thing, but where the heck is it??

Here's the problem.  I'm driving home over lunch today and the temp reading get's 3/4 the way up to redline.  Weird....never done that before.  So, i crank the heater on full blast to release some hot air and NO HOT AIR came out, only cold air, like the A/C was on!   It looks like the temp gets hotter the faster I go, but when I slow down/slowing down the temp seems to ever so slightly drop.

I get home and pop the hood... the antifreeze was obviously boiling and shooting out the vent by the radiator cap.  I then notice the DEX-COOL resivour by the battery has nothing in it but a few drops!!  I ran up to O'Riley's and got some more DEX-COOL and filled the resivour..  followed the directions of letting the engine run for 10 minutes and then check the resivour again.. did that.  But the resivour level didn't change a bit.  it's like it didn't pull in any of it!

I already checked the fan/fan clutch and it passed the "spin test."

i'm thinking it's gotta be the thermostat......  I just need to find it!

Thanks for any help!

Ok, so I found the thermostat...replaced it....and it appears to be holding it's temp at the correct level now.  Only once today when I was driving did the temp shoot up to about 220 but it's like a switch flipped on and it went right back down where it should have.  Cures that problem, but now I got something else so I'll start a new thread.