hi tmoc,
not sure what your initial problem is but maybe try simply removing the tstat for a while. this will help to tell you if the rest of the system is working properly since it will necessarily be at maximum cooling ability. take the car to a steep long hill on a hot day and watch the performance. run the ac too if you have it. with the fan on / cycling, the system should be able to maintain a steady mid range under any load.
the engine controls are set up for a specified range of operation and changing the tstat temperature will have systemic consequences which will be hard to predict or account. imho, the factory designed and balanced the components very well and terrific mileage and longevity are the result. i recommend the oem tstat but i even had to replace a new one of those because it was not calibrated / performing within the original range.
harbor freight sells an ir thermometer for about $26 on sale. they are quite accurate in my limited experience and you can easily get temperatures from many spots on the engine and cooling system.