I installed my gauges before I did the transmission mods, it runs maybe 10 degrees cooler after the DTT mods, but the thermocouple was originally installed in a test port, not in the bottom of the pan so maybe it reasonable to see a different before & after temperature.
Anyhow, I don't think my temps are too hot, but I would like them cooler. I don't run a synthetic fluid, I use valvoline ATF, comes in a blue gallon jug I buy at Checker auto. My DTT installer says DTT says use the plain old ATF, but change it every 10,000 miles if a lot of towing is done or 15,000 miles if not a lot of towing. It is pretty easy to drain, TC also has a drain plug, just need a BIG drain pan.