I know this is an age old debate and to some extent a matter of preference, I would like to know if plowing in low helps to keep the tranny cooler?

 

Although the following article is about pulling and not pushing, it might explain the advantage of gearing down. "Let the lower mechanical gear ratio inside the transmission increase the engine's torque and power to the rear wheels rather than letting the torque converter do all the work. Keep the engine speed up."
http://www.canadiandriver.com/articles/jk/at_000724.htm

 

I use 4 hi when I plow. 96 2500 318 auto . boss 9' plow.