Don't measure if the UTH is working based on how cool or warm your snakes feels. He may be in the middle of thermoregulating, your temperature is much higher than his, so its not a reliable way to measure if it's hot enough.

A good UTH will keep a steady temperature when used in conjunction with a thermostat to control it.

Set the thermostat for the UTH to 92 degrees on his hot spot. Under the tub it will be much warmer, but we want his hot spot to be inbetween 90-94.

For the ambient (air) temps in the rest of the tub, his cool side should best be around 80-84.

If your still having troubles, try and give us dimensions of everything your using, and even better a picture. A tub should not be hard to heat up.