I hate to burst your bubble but generally cheap digitals are not very accurate either. An accurate analogue (+/-0.5ºF) is a whole lot cheaper than an accurate digital (+/-0.5ºF). Did you test the analogue against a reliable meter? Do not ASSUME that an analogue is 10 degrees off I have never seen one that far wrong yet, although I own a digital that is.
A snakes are very sensitive to temperature issues. Are you sure that you have a proper gradient? (80ºF cool 90ºF warm with ambient air temps 79-85ºF)