Originally Posted by croused
Yup, the tow/haul mode brake sequence is the best for downhills....very impressive!
as I deliver brand new units from the factories to dealers, both gas and diesel, I can attest that the 'tow/haul' mode only serves to shift 'later', allowing the engine and transmission to stay in a lower gear longer, giving you slightly more lower gear time both uphill and downhill - though, touching the brakes when downhill allows the transmission to downshift earlier providing more 'braking' and not having to use the service brakes(brake pedal) as often.
Even when towing a vehicle, which is most of the time, I've not seen the 'need' to use tow/haul mode as I'm not necessarily concerned about the speed up hills, but more with fuel economy.
The engine/transmission works very nicely down the hills, just touch the brake pedal when you are at the speed you want to try to 'hold' while starting to descend(crest of the hill)...
Diesels work similarly, though they have either Exhaust Brakes or Jake Brakes, causing the engine to automatically 'slow' while descending, while the transmission follows in a lower gear. Cummins engines typically have a 'Mode' button, though it is to provide the opposite of the 'tow/haul' mode on gas coaches - it provide the ability for the transmission to shift earlier, providing better fuel economy. My Palazzo has probably only been out of MODE for a handful of times in over 75,000 miles... unless you want to pass everyone on the way up a long hard grade, it's not really needed to come out of MODE.