Ahh, that makes sense (and makes me feel potentially better about my situation). I thought/think I am in the HG nightmare right now, but I ran mine up a pretty good pass (over the Blue Mountains on I-84 out of Pendleton, Oregon) and it ran just fine on the temps. It heats up just a bit (to 105 deg C) when I am on the flat terrain. I just started a new thread regarding this issue.
Reporting mine was the t-stat too (aftermarket garbage) not a subbie. By the genuine part for the t-stat…..