The backlight manager on the Touch pro is not the best, so 1 member from xda-developers, nik3r made LUMOS, a complete HTC Auto-Backlight replacement. The 1st time you install it, will calibrate, just follow the onscreen instructions. That’s it. You can also put in exceptions for programs like GPS navigation etc, that you want the backlight to stay constant e.g. Tom Tom etc.
Check it out here at Xda-developers