The transmission should put you in the correct gear for going uphill. You'd want to use the shifter to select or "lock out" other gears depending on the grade, for example, if the transmission is indecisive and keeps shifting up and down, you'll prolong your transmission life and improve cooling by selecting the lower gear and/or shaving off a little speed and not letting the transmission shift up. When in doubt, run a slightly higher RPM, again, to help with cooling, especially for the transmission. Transmission cooling depends on airflow and fluid circulation, same with the engine and its hydraulic accessories.
On downhill grades, you want to use gears to assist with braking and maintaining your safe speed, which is generally a little slower than you ascended, and being mindful of any lower advisory speeds like on downhill curves. How fast did you go up the hill, and in what gear? You want to go down the hill slower, and one gear lower. You want to keep your foot off the brakes as much as possible, and when you do brake, do so intentionally. Never ride or feather the brakes as this generates heat and can damage your brakes, warp rotors, and rob you of stopping power when you need it. If you keep having to hit the brakes to shave off speed, grab the next lowest gear. It's alright if you're high in the RPM band, like 4k, 4500. Your "braking horsepower" from compression in a gas V8 tends to be high in the RPM band just like power is.
On those Ford transmissions, first turn off Overdrive if there is a switch. Then, start selecting progressively lower gears using the gearshift lever to downshift or lock in the desired gear.