Our Class C has the 6.8L V-10 and I have added a Scan Gauge, specifically for trans fluid temperature (among the many other wonderful things the SC does). You can make great use of and control your trans temp by engaging the Tow/Haul mode. Even on seemingly low grades the trans temp will creep up even though the transmission is not hunting. As you notice the temp climbing lock in Tow/Haul and the temp will immediately start to drop, usually 6 to 10 degrees as the transmission becomes more efficient/provides greater cooling. If your rig does not have Tow/Haul mode simply locking out O/D will do much the same thing.
Works for me.
:C