NO,NO DANG WAY!
The transmission control module is smarter than who ever told you to "manually shift" the auto.
Use the Tow/Haul mode and all will be fine, it's what I did with my 2010 in Colorado last year when coming down from Eisenhower tunnel.
2016 F350 6.7L LB CC Reese 28K 2014 Chaparral Lite 266sab
"Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety." 2014 19 days camping 2015 17 days camping201620 days camping