Michael,

I think the 8V92 engine for some reason requires strict adherance to the coolant maintenance schedule, and even with that it tends to plug radiator cores. That is my personal experience only.

You should run in the 180 to 190 temperature range and when pulling long steep hills the temps should stabilize at 195. You don't say if you have radiator shutters, but my comments assume if you do they are functioning as intended. If there is a question turning two valves locks them open so they are not part of the problem.

Unlikely, but just verify the fan is not slipping. The engine has two thermostats and they both have to function as intended. Ironically the gauge only registers on one side. It might be worth checking them to verify they function. If all else checks out you are looking at recoring or replacing the radiator. Don't delay this because the temps you mentioned are excessive and you are very close to having the DDEC start to shut you down. You can turn a 8V92 into an expensive paper weight very quickly with over temp conditions.