At 35 mph in second, the 3.0L V6 diesel in our 2007 ML320 CDI has enough back pressure to control the descent on a several mile 6% grade into the Salt River Canyon just south of Show Low, AZ with the 23D attached. It had all the necessary power to go up the mountains on the East coast, as well as on I-10 coming back from Los Angles, CA with the 25FB behind.
My biggest concern is stopping on descents more than going up. One may find there is nothing left to stop with if they ride the brakes going down mountain for several miles.....
WBCCI Life Member 5123, AIR 70341, 4CU, WD9EMC
TV - 2012 Dodge 2500 4x4 Cummins HO, automatic, Centramatics, Kelderman level ride airbag suspension, bed shell
2014 31' Classic model 30 twin beds, 50 amp service, 900 watt solar system, Centramatics, Dill TPMS, disc brakes, 16" tires & wheels