I took mine on a 300-mile summer road trip a few years back, and had no issues with T-case overheating, but I almost never exceeded 50 mph indicated, and I have Amsoil 75-110 oil in it. Exhaust heat got the floor hot enough to melt a plastic tool case, but the transfer case (with that exhaust right next to it) worked just fine.

Based on my experiences with a diesel-converted M37 running the same t-case & 4.89 gearing & this truck, I also believe avoiding heat-related issues with the transfer case is all about keeping drive shaft RPM below a certain figure: I could drive that M37 all day long at 65-70 with no problem because of its taller gearing, and 50 works fine in the M715 with stock gearing. It might put up with a higher speed, but I’m not interested in trying it.