Tranny temps: how hot is too hot?

When I first got my 07 tahoe, the temps during the first pull (short trip, flat lands) spiked up to 200. I then added the additional factory cooler (which I am guessing you have already) and the temps now stay around 190. Grade, outside temp and humidity, all have an effect on this. I think the highest I have seen is 205, during a climb, or during a high temp high humidity situation. This also occurred directly following a slight increase in engine temp, before it fell back within normal range.

I think your temps are fine. When I see 200 I start paying attention, just to be sure it comes back down, which it always does.