I have a 2007.5 6.6 with 6speed Allison. I will be towing a 35ft travel trailer and want to know if I should invest in any upgrades for my tranny?

transgo jr and a better cooler would be a great addition.

I tow a 12K 5er. On a steep, very slow pull in hot weather, the trans temp would push the red line — because the converter does not lock up. The addition of a deep Allison pan, a Mike L. cooler, and an Allison approved (TES 295) fluid did the trick (all were suggested by Chevy and Allison, as they know of this issue). I used Mobil Delvac ATF. The deep Allison pan is actually a stock Allison pan that can be gotten inexpensively from an Allison dealer — along with the deep internal filter. The entire job is a Saturday morning or less.

I wasn't aware there was a Mike L cooler available for the LMM trucks. Is this true?
Just talked to Mike L
NOPE! Nothing available for the LMM trucks yet, and "won't be for a while"

Tow the trailer first and see how the truck pulls. Later! Frank

Probally a cooler, deep pan, and some good trans fluid should do the trick