Do you have duals? I have an inchworm crawl box and a marlin 4.7 rear case and I notice quite a bit of heat coming though the shifter. If I crack a window it really pulls the heat. I think in my case it related to not having the floorboard completely sealed back up. I think there can be a lot more heat than most people notice, but I think you should be able to touch it without burning a finger at normal operating temperature. Compare it to other components like the transmission and differentials to feel what's normal.
When a previous crawl box locked up from a bad bearing it was so hot that when I got within a few inches of the case and realized I'd melt something if I made contact. When I pulled the shifter off it smoked a bit from the inside. In that case, I could touch everything but the crawlbox.
