2008 957 V6 3.6 Temp Gauge not working. Thermostat replacement?

[mhariush]

I have a 2008 V6 that is throwing a check engine code P2181 which appears to mean the thermostat is stuck open.

The temp gauge does not work. So I changed the temp sensor at the back of the block, and it worked for a brief moment. discovered that there is another sensor near the radiator, changed that one too, and it was working for day or two before stopping.

I can't find any diy repair guides for the thermostat replacement on this V6, and apparently, the factory specifies dropping engine and transmission, which I can't do at home.

Has anyone changed their thermostat on a 957 3.6L V6? Did you do it at a shop and what would this run usually? Or were you able to access it without dropping everything?

Any other things I should try before going to the dealer to have it inspected?