I'd ask for any records to see when/if any or all the following has been replaced:
transmission and torque converter, lift pump, high pressure fuel pump, injectors, ball joints, all the steering linkage, steering box, heater core, hvac doors, rotors, front hubs, and axles service along with all u-joints.
That's a good start. And I'd only ask any of that if the floor, rockers, fenders, bed, and chassis isn't rotted out. No sense wasting your or sellers time on a rot box.
If you're not familiar with these trucks I'd find a mechanic or enthusiast who is to help you inspect it. Good luck in your search.