Of a few issues.

1. Your substrate layer is too thick for a UTH to work properly. It needs to be ½" thick or less.

2. Your thermometers aren't reading the temperatures in the right place. UTH's don't heat the air in the cage, only the surfaces that they are in direct contact with. This means you need a probed thermometer like this one:

http://www.walmart.com/ip/Acu-Rite-I...ndingMethod=rr

The probe needs to go on the floor of the cage directly over the UTH.

What is your thermostat set to, and where is it's probe?

Based on your room temperature I think you should be able to get away with just the UTH.