ok, this is kind of embarrassing, but I checked again with the heat gun and I think the problem was I was shooting through the glass when I measured the UTH area. It's like 122F square in the center of where the mat is, and 70F where she is now, pretty much the middle of the tank. So that would explain why she never goes over to the hot side!! So I'll stick with the UTH I have, and get the thermostat for it and set it to like 90, and that should be all set. Ambient temp says 72F and the thermometer is an analog one, and it's near the top in the middle of the back wall. How can I get the Ambient temp up? I have a 100W heat bulb going all the time resting on the screen on the left side.