It's a 20 gallon high and the basking spot is 97-99. The temperature on the warm side is 89-81. And on the ambient side it 77-81. My little guy is thriving on just a heat lamp. It doesn't fluctuate like a an UTH so I don't need a thermostat.
A 20-high glass tank with those temps from a heat lamp is creating a desert environment for a snake that needs high humidity. You need to dial those back and cover the tank with something to hold moisture in.