Where are your digital thermometers placed? You should at least have one digital probed thermometer placed directly over the UTH right on the glass, under the substrate. You want to measure the hottest point the snake can reach at any given time. You should also have another thermometer on the cool side just above the substrate level.
The hydrofarm thermostat from Amazon: http://www.amazon.com/Hydrofarm-MTPR...0858892&sr=8-1 is inexpensive but will get the job done.