If he isn't screen climbing around the cage all the time and just sits right under the basking bulb it most certainly is an issue with his temps. may or may not be useful but, what I use is a reflector dome w/ a 70 watt halogen bulb that I position pointed towards my chams basking branch at an angle (not just sitting on the screen directly), so that my chams don't accidentally burn their self, it's easier to create a temp gradient rather than the basking bulb just beaming down on one spot of the branch, and also to position the uvb and basking bulbs so that they're both above his basking branch to mimic the sun.
A pic of your set up is always much appreciated !