Stick on thermometers are wortheless get a digital one and put the probe on the hot spot and the main part on the cool side so you can measure both. Are you usuing a UTH(under tank heater) which should be used with a thermostat to regulate. I think you tank is too tall as well. I use an oil filled heater in the room with my snakes on a thermostat to keep the room warm. 67 is WAY too cold. You need to get him closer to 80 on the cool end.

You could put him in a tub in the tank and then use a Radiant heat panel to get the ambient temp in the tank at 80(instead of the whole room) and then put part of the tub on the UTH to get a warm spot of 92. I do a similar set up for quarrantines sometimes. Tubs are easier to control than glass tanks. They dont need all that height, just makes it harder to control temps and humidity.