I agree on the stock gauges behind inaccurate. Also, I'd like to meet whomever designed the wiring and circuitry for the gauges. Almost every 5.0 I've owned has the same problem of the temp gauge going up 10-20 degrees when you put the lights on. On my current one it goes from about the middle of m-a to almost 1/2 way on the gauge.
Regarding the stock vs 180 stat. I dont think there is any harm in running a 180 stat, but engines tend to operate more efficiently when hotter - obviously to a point- better mpg, oil flow, etc. My point was too often people think swapping to a lower temp stat will solve some other cooling system issue such as overheating etc..
The bad thing is i do have an aftermarket gauge in dash and also a radiator cap with a gauge on it and they are relatively synched which really get's me. I am wondering if the ECM is on its way out or i have a cts to ecm issue. I also put a new heater core and thermostat rating at 195 degrees to jsut make sure there was nothing to low put in there and still the same. She is parked for the winter so i ahve time to try and figure it but am running into some other issues which i am about to make a new post for.
Your ECM has very little to do with coolant temp.(unless you have a car with an electric fan controlled by the ECM.) If your fuel mixture was way rich or lean it can change the temp a little. The temp gauge on the cap is worthless. That's like the coolest point of the cooling system. If you do not have an electric fan the fan clutch is probably seized or you don't have a fan clutch. If it is an electric fan wired to run constant that could be the issue. As for the thermostat drilling thing listed above, most auto parts now sell thermostats that are designed to fail in the open position so you don't overheat. Well worth the extra dollar. The hole that is in some thermostats from new is to allow air to escape when you are filling the system so you can fill it without an air pocket.