That's a tough question to answer. It depends on a lot of things. Quality of fuel used over its life, climate, how much it has sat, how much of its life it hasn't been full, etc. It really comes down to how much moisture it will have been exposed to. There's no way to say "23 years old, that means it has X years left." It's pretty common for a fuel tank to last the life of the truck though.

I can understand being paranoid about all your brand new parts, but if you were to see the varnish and crud that will build up inside them as they get used, you probably wouldn't care about the fuel tank anymore. The fuel filter catches most things that would cause a stuck float, etc.

If you're really concerned, you can drop the tank and take it to a radiator shop, and have them clean it out and tell you what came out of it. If this were my truck, I wouldn't worry about it. I am of the "if it ain't broke, don't fix it" variety especially when fuel tanks aren't cheap, and since the fuel filter offers protection. Your call.