temps for engine oil, trans oil, differential
 

1969 firebird LS swapped, I would like to know operational temps for engine oil, trans oil, differential? This is my first modified car. Need to know which temp, 165 or 185 cooler temp by-pass, is correct for these oils

Need more information. What engine, and what is done to engine? What transmission? What rear end, and what's in it?

The engine is stock 2008 Silverado LY6 6.0L, Trans 6L90 and diff is a 1969 12-bolt. This is the first time I will have gauges for the items and have no reference for what they should be or to know I'm in deep DO-DO.

I can not say what your oil should be, but I would have liked to try to keep the motor not above 230*F if possible. And stable.
What I do know, is that it is almost impossible to get a "too big" oil cooler if you are going to track it and drive hard.

On my GTI I tried a "cheap" semi-synthetic and "good" Synthetic oil, when driven hard, the Semi got up to about 280*F, with Fully Synthetic it was about 200*F. Dont remember viscosity, but big difference in temp!!
There are probably people here with much more experience.
But there is something about getting it warm enough to burn off water and contaminations but not too warm to destroy the oil. I would rather have a bit cold oil than too hot myself, I think this goes for all oils.