I swapped out my small Haydin Rapid Cool plate and fin style trans temp for this much larger tube and fin Flex-a-lite cooler. The Hayden was 8" x 11" x 3/4" and and rated for about 20,000 GVW (which you would think would have been enough). This this one is 11" x 18" x 1.5", and rated for 32,000 GVW (it is part number 4232). Took the truck out yesterday in the middle of the afternoon while it was really hot, and tested it out. Usually, I would have been up to 180-190 degrees in no time. I ran about 165-175 all day while driving around doing my shopping. Next test will be this weekend when I pull the camper again. Last time, I saw temps over 210, so I am hoping this one can keep up better. If not, my next cooler will have a fan.

Here are some pics of the old one and the new one for comparison.

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Pretty pleased with this change so far. I towed the camper this weekend up many of the same mountain passes I was on a month ago with the smaller cooler, and my highest temp reading was about 25 degrees cooler then it was the last time I towed. Outside air temp was cooler too, but I think this new trans cooler is doing a better job overall. Temps driving around town the last few weeks have also been cooler on average (by about 15 degrees).