2007 Z71 transmission guage reading

I've been monitoring my transmission temperature the past week in preparation for installing a tranny cooler this weekend.  The normal operating temperature in current 80 degree Florida weather has been 170 degrees on average.  However, the odd reading I get is when I start up the truck after being parked all night in a garage.  The gauge immediately shows 90 degrees upon start up.  Does anyone else get a similar reading or do I have a sensor issue?   

My transmission temp gauge bottoms out at the 100 degree mark on the dial.

There is no 90 degree mark on my gauge, so I can't help you there.

The operating temp of 90 degrees above outside ambient air temp is what I usually run, so in that regard, I think you are in good shape.