Your humidity problem is most likely stemming from the use of the lamps. They will suck the humidity dry.

Most people can usually find a way to heat tanks just fine using only UTHS (2 usually). Although it is possible to just use one UTH if your room temp is around 80*.

I don't remember if you have said it before but what kind of thermometers are you using to measure how hot it is?

Sounds like the "thermostat" you have isn't really a thermostat. If it was, it would have a probe.