I pull a fiver RV with F250. When going up inclines, especially LONG ones, i turn cruise control off, use foot control. I drive like egg between foot and gas petal. I noticed when doing long climbs, boost increases, with oil, water and tranny fluid temperatures increases. Not to mention the extra load imposed on the engine bearings. I found I could slow down, watch temperatures while going uphill, seek a speed where HH fluid temperatures do rise, seek stability of temperature at a reasonable towing speed.
Know of other owners who use cruise control while towing, let er rip going uphill, and suffered blown engine. I can afford to slow down, but not a blown engine. Especially if truck is a 2011 model, with many of the known faults by Ford at play.