theres been a lot of talk about heat and lifespan of slush boxes on the diesel board, basicly the useful life of the tranny drops by half every 25* over 175* modern trannys with lock up converters don't make nearly the heat while locked up, so most of the diesel guys run a switch to control the lock up and get it locked faster when hauling and when using a exhaust brake, one guy wrote a article about driving his 30' dodge cab/cummins powered motor home to the top of pikes peak and a combo of a locked converter when he wanted it a kit that lets you run the 4wd transfer case in 2wd low range and a exhaust brake let him get it to the top and back down without roasting the brakes or tranny, he said in previous attempts the tranny fluid would get in the 200s in no time unlocked and take a couple minutes at a fast idle to get it down below 175* on the side of the road with the converter unlocked