I'm not sure this will help, but I can say that I was using one of my N900s as a hotspot fairly regularly last year. The only time it developed problems was when I would drive it too hard; it would start losing connections with continuous data transfers that lasted upwards of an hour or more. This was probably due to overheating, as the phone was always hot to the touch when these problems occurred. (I avoided large data transfers with the hotspot after that.)

This was using Joikuspot, running on vanilla PR1.3.1.