What is the trans temp supposed to run on a 2009 Tahoe Hybrid

temp gauges are suppose to run from 120 to 170, any higher than that have your coolant checked or drained and replaced, if it's still not helping, then your thermostat might be stuck or water pump going out, does it squeak when you start it up for a while in the morning or during driving if so water put, if your temp is yo-yo'ing then thermostat, if none of that to much water in your radiator or your engine oil needs to be replaced oil change needed, or less water pure almost antifreeze, works real good.

No modern car after 1995 should run at less than 205F for proper emissions control and performance , normal operating temp. for trans will be about the same depending on conditions. Are you towing with it?