Engine/Transmission (1998.5 - 2002) NV4500 how hot is too hot

[STPH]

I just put a transmission temp gauge on my NV4500 and registered a temp of 170 deg on a 100 mile trip from Red Feather Lakes to Denver. My question to the members is at what temp do I start to get nervous? I pull a 6000# 5'er in the mountains and want to utilize OD as much as possible. Need input! Thanks. steve