Replacing thermostat on 1996 GMC Yukon

After a bit of research, I've come to the conclusion that the thermostat is stuck open because the engine never warms up, and I never get any heat.

Can I get a diagram of how to replace the thermostat on my Yukon? Me love you long time

Well I was going to give you a picture from compnine, but apparently they shut down...

Anyways, it's a real simple job, only involves two bolts. All you do is follow the upper coolant hose (connects to the upper drivers side of the radiator) to where it connects to the top of your engine. It connects with a metal elbow piece that has a sensor screwed into it(that's your coolant temp sensor). That elbow is held down by two bolts (i believe they are 1/2'' size). Just remove the bolts, pull up the elbow, and you'll see your thermostat right in the opening on the engine. Pull out the old one, put in the new one, bolt it up, and you're done!
p.s.-be prepared to leak a lot of coolant.

^^this....just be sure and clean off any gasket that may stick to the manifold prior to putting the new thermostat on

When you refill the radiator, dont fill it all the way to the top. Use a flashlight to look into the radiator, fill it SLOWLY till about 3/4. This way you will let the air bleed out of the top of the motor. You might hear a faint whistle of the air going by the stat with the engine off. If you fill all the way to the top, when the engine warms up, it will expand the air in the block and push out coolant at the cap and make a gurgling mess. Also if you fill to the top, it will trap air in the block.

After you start the truck and the engine starts to warm up, you can feel the upper hose, and when it gets hot you know the thermostat has opened .....for a few seconds anyhow. You will see the coolant level in the rad drop. Let it run for a few more minutes and then fill to the top, but not topped all the way till it spills out (2 inches low from cap is good). A little air is ok, the overflow will take care of the rest after you put the cap on. Whatever coolant you decide on, mix it with distilled water.
Dont forget to add to the overflow tank....it will draw from there to fill completely when the engine cools and then warms back up.

Thank you all for the advice, I changed the thermostat this morning, the old one was in very bad shape, new one works great, I have heat for the first time in 2 years and it only took me 20 minutes, I didn't leak that much coolant, but I had it topped off at Jiffy Lube for free since I bought a coolant flush from them a couple months back. Engine quickly warms up to 190-210 in around 5 minutes at 50c ambient temperature when before with the bad thermostat, it would rarely, even in hot weather, get above 120