I usually use the racks from Reptile Basics and I'm used to setting the thermostats up really high in order to get the temps in the tubs up to 90+. I received a large home made rack from a friend and I finally got the thing put together a few months ago. I set the thermostat at 86 just to see where the temps sat at that setting. At that temperature setting, the rack heated up to exactly 86. I added in the tubs (not all of them, only 4 out of the 12 or more it can fit) and the temps went up to 94. I lowered the temp setting on the thermostat to 84 and the temps sit at exactly 92.

Could it be the thermostat that makes the temps higher than the setting?