Without seeing your set up or knowing really anything but what youve said is:
Your basking area is not acceptable to him.
You humidity is too low.
Keep in mind, with an overall HOT cage, the monitor cannot have control over its own temps. This is therefore forcing him to be hot all the time, and can be stressful on the animal.
I do know of a zoo that keeps steady ambients of low 80's- low 90's, with no "basking spots" and they have actually bred and raised a couple species of varanus this way.
Being that this zoo is in a tropical climate though, the humidity is always at like 75% whether you WANT it to be or not! Haha
Their cages are also huge, with lots of options and lots of different types of "hides". I would imagine that there are temperature variations within the different areas of the cage, simply bacause of the way different materials conduct heat.