set cruise control go into tow haul and let the engine/transmission decide what to do on the way up. and if cruise works going down (which the allison on late models do) turn on exhaust brake and set cruise for desired downhill speed and let it do it's work to hold you on the downhill side.
sure, you could use the manual transmission mode, turn off cruise, but I've never found that to be an advantage, if anything a disadvantage. I just let cruise control do it's job. It's been very very very seldom where cruise wouldn't hold the speed I wanted, or very close to it.