Some ROMs and phones don't like ULV or LV because it can result in bad memory writes if there isn't enough voltage. This causes the same operations to be repeated over and over until they are done correctly, which causes heat and rapid battery drainage. I would try switching to a standard voltage kernel. I am on Slayher's 1 GHz downloaded right from ROM Manager, and have had good luck with it all day (69 Fahrenheit idle temp). I am still experiencing the drop to 1X though.