1991 F150 fuel tank problem

A friend of mine who lives in a very hot environment bought used a 1991 Ford F150 which was sitting undriven and not started for 3 years. He thinks the gas in the fuel tank has changed composition and is causing problems with running.

Does old gas in a fuel tank that has sit for 3 years in a very hot environment (TX) change composition and would it be necessary to completely drain the fuel tank to solve the problem????

Thank everyone for any advice!!

these days gas does not have a good shelf life if it has alot of gas in the tank i would drain it if not you could get away with just adding some preimuom to it and run it but three yrs i would drain it and start fresh with new filter