1986 Chevy Truck engine keeps dying

I can get the engine to fire up, but after about 45 minutes to an hour it just dies. It will turn over after that but jusy wont fire back up for a couple of hours when it cools off. It had been sitting un-used and not running for about 6 months before the problem started but ran good before that. The thermostat is new and the fuel pump works good I checked both of them