No shame in the discovery that treadmills are surprisingly poor facsimiles of reality. Anecdotally, I've observed that ostensibly identical treadmills with identical settings can have different perceived efforts, though the floor may have been sloped. Unfortunately, a 2-minute improvement in 5k time without an enormous training effort just isn't realistic. But keep at it; your athletic proficiency still exists even if it wasn't measured correctly last week.
And however bizarre the numbers coming out of a treadmill are, it is still vastly superior training to not running at all!
Well previously I had been playing ultimate frisbee or oritneering 7 days a week, so I hadn't been doing nothing. I thought the agility work associated with ultimate might be making a difference.