How's your fan clutch?
180 is ok, however, 195 as previously mentioned was more for lower emissions, increased performance and economy. A thermostat in general is for a quicker warmup. Cold engines waste gas, metal, and time.
Thermostats do NOTHING for overheating issues or controlling maximum operating temperatures. The setpoint simply dictates the lowest temperature that starts coolant flow through the engine, or basically, it only effects minimum engine coolant temperature. Think of it like a garage door. Temp hits setpoint, garage door opens up. Goes below setpoint, garage door closes. This is based on what the thermostat "pill" temps see. It doesn't care if you have a blown head gasket or other issues. It doesn't care if you have a copper or aluminum radiator or the coolest looking hose covers. Once it opens, its job is done. If you overheat, it doesn't care. It's only the thermostat's fault when it doesn't open due to a thermostat issue.
Have you checked the accuracy of your gage? So you put a new sensor in, which obviously could be off calibration slightly from your original one that died. I mean, if it was dying, who's to say it wasn't reading correctly anyway? It lives in a harsh environment on the head. If the wire is corroded or there's 40 miles of teflon tape keeping the sensor from getting a good ground (a mistake made more often than you think), your indication may be off. I'm assuming you have the factory gage in it, which is just a guesstimate of actual temps. Get an IR temperature gun and take some readings. That should tell you what's going on around your cooling system. You don't have to buy a Fluke brand or any of that super expensive junk. $25 can get you something you can use for comparisons.
You also have a little larger heat generator with the 350. Although your cooling system, if in good shape, should be able to handle it without issue.
If you have an air bubble in the system, that could cause erratic temps as well. If you've been driving it around, the air bubble should have worked itself out. If you're still adding fluid to the overflow, something else may be an issue. If your overflow tank is empty, you can't guarantee you have enough coolant to keep temperatures where they need to be. The rad cap is designed to burp excess coolant to the overflow when hot, but also suck excess coolant from the tank when cooling down to keep the system full. The only air you should have is on top of the fluid in the overflow tank.
