If it cools down quickly after the climb, that would certainly say the radiator was not maxed out for water cooling. We have found that a short steep climb will raise the trans temp, but much less on the water. In that case the trans temp drops right away after the climb. On long climbs, the water temp gets hotter, and then the trans temp takes a long time to drop, as it is tracking the water temp in the radiator. It makes sense, I think, because you have van that optioned a 454, so lots of room for a big radiator, and diesels put considerably less heat into the water. Sounds like you have very nice combination.