However when I finish my run, and then go into my 1:30 cool down, again at 4mph, it feels leisurely, like I'm strolling along.
Speed is all relative. I watched some guy in Seattle running at 8mph and it looked like he was coasting, whereas I probably look like a lumbering rhino at that speed. However with my long legs, maintaining a 4mph pace is fine, while that gets my little girl into a slow jog.
I can tell what kind of day I've been having by how that first two minutes feels. When I've been sitting around or working at my computer, it feels fast. If I've been walking around doing things, like feeding horses or working on fences, it doesn't feel so bad.
I wonder if that's the case with other runners?