a fellow iowan??? welcome to FTE! Like the other guys said changing the fuel tanks is easy enough to do and a common problem. If you are thinking about taking it on a longer trip and it's slow you probably don't have much to worry about but i would change it and be cautious if it were me. If you are just thinking about buying this truck I would try and barter the seller down a bit to cover the cost of repair and if you are looking at fuel pump and tank you are already at $200+ for parts. whether or not to "run away" depends on the truck and what you are paying for it. If you add the specs for the truck, condition its in, and the price... We can probably advise on to buy or not...

PS the 87-91 trucks are pretty easy to work on...