That is your first problem....don't ever guess your temps. You need to know what they are otherwise you are going to have a severely burned snake. I suggest a digital thermometer, or a temp gun. This is the one I use and I live by it. Do you use a thermostat to control the UTH, because I can pretty much guarantee the hot spot is well over 85, and closer to 110. My small zoo med UTH was exceeding 130 without a thermostat....
Edit: Just read about the reptitemp...I ordered that when I first started, set it up, used it for about 1/2 a day before it almost went out the window. I promptly sent it back and got my money back. IMO a real thermostat is well worth the money. I know some people use them without issue but I personally loathed it.