I know that my peak operating temps lowered a significant amount with using a lower t-stat, but I cant explain it, must be impossible
That's what I meant about your Camaro being different than a 6.5TD ... in your Camaro, the cooling system capacity is much greater than your engine's heat-generating capacity. Not so in these trucks... The cooling system capacity is not as high as the heat-generating ability of the engine when working hard.
For instance, taking the thermostat right out in your Camaro will let it run REALLY cool... but let's say you tried that in one of these trucks - first, it would run crappy (diesels don't like cold), but as soon as the engine started pulling and generating heat, the temp would climb back up again.
The only thing a 180* Tstat in a working 6.5 will help with is the time it takes to overheat... if you can get to the top of the hill and start down before the inevitable happens, then you are OK, and the 180* Tstat will give you maybe an extra 20-30 seconds to do that.
On long hills, you're still hooped.
If you want to replicate the scenario in your camaro, put a sheet of cardboard over the rad and try pulling something hard, uphill, with both thermostats, a 180* and a 195*.
You'll see what I mean.