That's what I'm thinking. Plus, are you controlling the UTH with a thermostat? I don't think changing the feeding schedule had anything to do with this, neither does feeding 6 days after instead of 7. Some people feed their snakes every 3 days, and some others will feed theirs every 5, so I know that it not the case. I would consider getting a digital thermometer, those are very accurate. Stick it on the bottom of the enclosure right above the UTH and tell us the temps. If you do not have it controlled by a thermostat your snake can get burns and can also die from overheating.