I have a 1997 K2500, 208,000 miles, with the 454 (Vortec 7400 L29), and it has overheating issues. It can run for at least 20 mins no problem as long as I'm gentle with the throttle, but then it starts overheating. I'm guessing the main problem is the head gasket, since the exhaust is white out of one of the tailpipes (it seems the 2 sides of the V8 have completely separate tailpipes) and smells sweet. In order to keep it cool, I've had to refill the radiator with water every now and then, so it's definitely going out somewhere. In addition, when I had it by a mechanic he told me the radiator is gunked up, and I've noticed the coolant reservoir is as well. A friend pointed out it may be because other junk is leaking into the coolant when it flows back into the tank. Whenever it starts overheating, steam comes out the driver side of the radiator (not from the radiator cap). Also, once, when it overheated particularly bad, something orange (rusty coolant?) sprayed everywhere on the driver side of the engine bay, and I still have no idea where it came from.
My question is, where do I start? Do I start with taking apart the top end to check (and replace) the gasket, or is the problem possibly something else? Do I replace the radiator or is there a way to clean it out? As long as I don't need special tools, don't need to spend on anything other than parts, and can leave the engine where it is, I don't mind doing work - I just have no idea where to start. Any tips, guides, ideas, manuals, etc. will be appreciated.

 

I found this video and was wondering if it applies to my truck. It's for a 350, while I've got a 454, but it looks pretty similar. Can I follow it, or are there some big differences?
Also, I was looking around and found out about head gasket sealer. Would that be a good solution for me to try? I feel though that it would just gum up in all the wrong places - true or not? Any experience using it?