When beginning to descend a grade, you should be in a gear that will limit your speed to the maximum speed you want to go. During this process the engine/transmission act as a brake. The whole point is to descend at a controlled safe speed where you use your TV/RV brakes minimally to avoid over speeding your engine/transmission. Exhaust brakes are terrific for downhill grades and I highly recommend them.
If you're asking at what speeds can you safely downshift for each gear, I don't have that answer but bad things can happen to your engine/transmission if you downshift above maximum rated speed for the selected gear. It's a good question and one best answered before you need to know the answer.
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2010 3150RL
LevelUp, Dual 6 volt batteries, Progressive Industries EMS HW50C, Honda EU2000i Generator, Bridgestone Duravis R250 tires, Torklift Glowstep Revolution Stairs, LED Tail lights
2015 RAM 3500 Laramie SRW LB CC Cummins 6.7L Aisin Trans B&W RVK3600
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