I'll attempt to respond to several previous posts here. The beauty of the Scan Gauge is that you will know exactly what your trans fluid temps are. The first time you run with the SC on even a slight grade you will be able to watch your trans temps creep up. Engage TH and they will drop 12 to 15 degrees in just a couple of miles.
Trans temps (I am taking about the late model V-10), will rise and fall with the terrain, load and ambient temperature. Watch for trends and adjust accordingly. A brief climb up to 220 - 224 on a long, steep climb {like we encountered coming up from Panamint Springs climbing up the massive grade in Death Vally last September, towing 1,000# of motorcycle and trailer, temp 104 and climbing}, is not a disaster but you better be in TH and back off the throttle.
At the top of the grade the temp quickly dropped back into the 1995 to 210 range with no discernible harm or foul. So long as the temps fall commensurate with the change in conditions things are working as they should. This also applies to your engine coolant temps.
Engaging TH locks up the torque converter and/or dramatically reduces slippage which equals friction which equals heat. On downhills, especially long steep grades - think 6 to 8% over 10 to 12 miles - you will be able to safely descend in TH, probably without touching the brakes. An additional benefit is that you are not burning a drop of fuel as the flow of fuel to the engine is cut off.
Most folks do not use Tow Haul nearly enough. The weight of a normally loaded Class C is more then enough of a load for the rig to substantially benefit from running in TH mode. Obviously if you are towing anything or loaded heavy, engaging it is a no brainer {only those with no brains don't}.
Running in the TH mode will not have any significant impact on your mileage but it will protect and prolong the life of your trans mission. Use the SC {or any other reliable trans temp gauge}, to confirm that it is time, usually overdue to engage TH.
Works for me.
:C