[MiraclePieCo]

How do you know it's a head gasket? What are the symptoms?

You're right: replacing head gaskets is a big job. If your heads are cast iron they are HEAVY and hard to lift when bent over a fender (I lift them out with my engine hoist). Lots of things can go wrong and you might have to do it again (my record is three times - twice). Knowing how much work it is, I'd guess that my mechanic would charge $600 (8 hrs labor @ $75/hr) - but typically everything costs twice as much as I think it will. If a shop does it however, any re-dos are on them, and you can get the truck back on the market that much faster.

I watched an episode of Roadkill where they literally fixed a cracked head with one of those chemical additives (K-Seal). Not saying I recommend that, but I'd be remiss if I didn't at least mention that option. It's what a used car lot would do ;-)