I had the same problem with my 2008 Chrysler minivan behind my DP. At the time in 2008, Remco had no solution as the problem did not start until you towed about 2 hours in ambient temps that were greater than about 85 degrees. Like you, I was forced on many trips to run the minivan at idle behind the DP which also caused me to disengage the Brake Buddy so the brakes did not lock up.
I still have the minivan with the Remco setup, but bought a Jeep which is MUCH easier to tow 4 down. Based on your info, I may give Remco a call to see if they recommend a fluid drop for my transmission too.
Tom and Katharine
'07 Winnebago Tour 40TD, 400hp Cummins
RVing for 19 years & 150,000+ miles