We just upgraded our 2003 Chev Tahoe to a 2018 Chev Tahoe with the trailering package and 6 speed transmission. We pull a 22' travel trailer over Colorado mountain passes to our camping places. With the '03, we usually had to shift into low gear to make it up and to control the descent. With the '18, I am planning to use tow/haul mode while pulling the trailer up the pass. For the descents, I am planning to use tow/haul and Manual mode so that I can control the speed of descent by shifting to the best gear. I read one post that said tow/haul engaged powertrain grade braking. However, I read another that said engine braking was disabled while in manual mode. Is it true that engine braking is disabled in Manual mode? I'm very confused at this point. Can someone please help me? Thanks!