it all of a sudden gave me a reading of about 95 psi in a 80 psi tire.
I'm sure you are aware that tire pressures will go up while driving due to heat. 15 psi on an 80 psi tire isn't terribly extreme depending on outside temp, sun, etc. And if the original psi in that one was just a little higher than the others, that could contribute too. It would be more revealing to know what the running psi of the others were in comparison to this one.