Well, after popping a code P0128 a few weeks back, I found the instructions and inspiration to change my thermostat myself last weekend. BIG SHOUT OUTs to :
Double D ---
http://forums.trailvoy.com/showthrea...ght=thermostat
and rbarrio --
http://forums.trailvoy.com/showthrea...ght=thermostat
Both methods were helpful, and once again, this site proves to be invaluable in the money saved on repairs, and the increased life of my TB!
I gathered all my tools as well as the new thermostat, 1 gallon of dexcool, 1 gallon of distilled water, and a new serpentine belt (to replace the original!!)
1 - My first step with all repairs is to disconnect the battery. I like to tie my negative cable back, just to make sure it does not contact anything while I am flopping around under the hood.
2 - Remove the serpentine belt. I used a breaker bar with a long pipe over the handle. It gave me plenty of leverage, and it was easy as pie to push it with one hand, while pulling the belt off with the other.
3 - HELPFUL TIP
to remove the alternator, I first removed the bracket, and then removed the two top alternator bolts. THEN, since I was working alone, I grabbed a tie down strap I had laying around, and wrapped it around the A/C hose that snakes in front of the bottom alternator bolt, and then fished the ends of the strap down through the left front wheel well. I pulled my battery, and used that to pull the strap just enough to keep the hose out of the way. From there, I could easily get to the bottom bolt. See pics!!
4 - Disconnect the wires from the back of the alternator, and then slide it/maneuver it to either pull it out, or in my case, move it enough to gain access to the thermostat, which should now be completely visible.
5 - at this point, it was easier for me to remove the thermostat while still connected to the hose. I removed the top bolt from above, and removed the bottom bolt through the wheelwell.
Be prepared for coolant to spill all over once you loosen and remove the t-stat. From here, I found it easier to turn the hose so I could remove the clamp and the old t-stat. Here is the old one... WIDE OPEN, just as expected!!
Old vs. new part. MADE IN CHINA.. on my Chevy!
Putting everything back together was too not hard, but like everyone else, I dropped the bottom bolt when putting the new thermostat on. I finally figured out I could wiggle my hand in there and start the bolt by hand, then go through the wheel well again to tighten it.
Here is the new serp belt. Make sure you get the right one. I have an EXT, and this one went on easily.
And here is my result! After a coolant drain and refill - No more SES light, and all the gauges look good... except the fuel gauge! haha.
I do hope this was as helpful to someone as the posts that inspired me to do this job MYSELF!! Now get out there and don't come back without some scrapped knuckles!
Sticky please, awesome tips, excellent pictures, and extremely clear write up. I just changed my thermostat at the stealership today. Scary price, guys, compared to buying my own thermostat. Didn't want to tackle the problem myself since I have 4WD and I heard its a lot harder to get the bottom bolt with the drive train in the way. But when it comes time for another new thermostat I will definitely try to do it myself. 
