185 to 190 is a little hotter than normal, an AC Delco 131-158 180 degree thermostat will close at 176F then open around 180 F . So your TCM might be looking for different temperatures then you reported.
How old is the Dexcool? It has a lifespan of just 5 years, perhaps a drain and fill and burp will clear things up when you install that new thermostat!

 

Oldblue
You should edit your numbers. 185-190F is the ideal temp range.
And your 178-185 statement doesn’t really make sense.

 

Yes it carries a 180° thermostat so 185f to 195f would be about right.

 

However, the time it takes to get from ambient to 178F is what the computer looks at.

 

Those are the numbers both my HHRs DIC’s showed. I didn’t make them up.

just drove to Smithville. 82 F out, the coolant warmed to 180F the thermostat opened and the coolant cooled to 176F the thermostat closed to start that cycle all over again

 

Yesterday morning it set a U0101 code. I believe it is looking more like electrical. All explanations I have read for this say, missed communication or complete lost of communication between ECM, and TCM. I have decided to take it to a transmission shop and let the experts figure it out. I will try to post what I found out, after evaluation of vehicle.
discombobulated.🤦‍♂️

 

Got car back. They are saying definitely electrical communication between ECM and TCM. Question. Anyone know if the ECM is supposed to be chassis grounded? Continuity tested TCM to negative and comes up closed circuit.

 

Most likely power to a module. They all go to ground on a pin.

 

You might go to junkyard and get transmission harness connector with 6-8” wire so you can check resistance of all solenoids.

 

Just got car back from transmission shop. Transmission is just fine this is an electrical communication issue that is probably going to be a nightmare to figure out.