All is well. I figured out why the temp changed. When it was up on the bar, I had an old hot pad between the uth and my countertop. The kind of hot pad that is a thin layer of metal crimped over a piece of cardboard, you know, for putting your hot pots and pans on. I stuck it back under the uth, and it's brought the hot spot back into the 88-90 range. YAY!