We have a Chevy 2500HD Duramax/Allison pulling 10,000+ lb TT. I always leave it in DR with the exhaust brake turned on and the cruise control on. The Allison tranny figures out what it needs. In the mountains, the cruise control will do all the gearing down necessary for the downhill runs. If it goes above 3,800 rpms, I might add a little breaking [exhaust] but rarely had to. To us, the Allison tranny is worth everything in towing.
2013 Silverado 2500 HD Duramax/Allison Tuned
Aviator Wright Flyer #1919
"First In, Last Out". 11B4Y
DAV, MOPH, VFW, 5/7 Cav,1/8 Cav Assoc.
11th ABN Pathfinder Co. N7MIP