Did the Blackbox have ports for the cooling lines? (Or did you have to drill and tap?) Does it have an internal pump? If not what did you use for a pump?It is suited to highway driving but it needs extra capacity to make it run cooler. As it is there is only about 1/2 quart of gear oil and there really needs about 3-4 quarts to keep it cool. Like I said in an earlier post my dad's black box made it over 2000 highway miles in just a few days on the 1/2 quart and it didn't grenade, it got hot but didn't fail. With the extra fluid capacity added there shouldn't be a problem. Add a reservoir, pump, and a finned cooler and the highway problem is solved.