454 Overheat or Sensor issue

Our 89 BFN 454 is running temperature between 190 - 200 in the lake. Thermostat installed is a 170 degree. (I have not pulled thermostat yet) I pulled the impeller and it looks great. Also checked all hoses for tightness. Removed the water strainer re- wrapped both input and output fittings with Teflon tape. Ran boat and let it get to 190 on gauge. I used a IR Thermostat and took several readings around the block. See below. Could I have a failing sensor or a true overheating problem.

150 - Thermostat Housing,    140-Intake,   140 - R Head front, 150 - L head front,
140 - R head rear, 145 - L head rear, 115 - intake, 150- Block front
130 - Block back.   155 - Block by sensor

Thanks......Would it help to install a 150 degree thermostat? Currently running a 170.

Thanks Pete.......I could not find the required temperature for a 454 in the PCM manual. Does anyone know what is recommended by PCM?

Thanks Mark......My Thermostat is a 170 installed by previous owner. I pulled it today and did the hot/cool water test and thermostat worked great. Re-torqued all hose clamps and I did find a raw water pump input hose that was not tight! Will test it again tomorrow.