I received a 600 Watt power supply unit this evening. I have some tasks I must perform in the next few days, but as soon as I install this power unit, I will test the game and let you know what happens. Thanks for your input, Dr. Disaster.
600 watt power supply was installed, and the problem is corrected!
MSI afterburner confirmed GPU never reached higher than 48 Celsius during 20 minutes of gameplay. Now, all I have to do is learn how to play the game, a LOT better.