It sound like you thermometers are reasonably good as they are the same. The ambient temps seems off how are you measuring it? 85-90 is quite high ambient. I usually would measure it by hanging the probe about 2-4 inches from the floor centre of the enclosure. We are looking for air temps.
Anya, snakes can tolerate easily as much as 100ºF with out issue. The problem is two fold, most heaters are not even and there is a good chance of a higher spots here and there. The second point is that they cannot digest food at higher temps. I know a few big breeders who during the hottest parts of the year when brown outs are possible don't offer food due to that. They can manage to escape with out a bun but cannot exist at that temp for a extended period of time. They become restless and run with a much higher metabolism and burn much more energy but at the same time they usually will not eat either.
