Turns out, I'm not slow after all and may, in fact, be building speed. Reminder that I may be pushing myself too hard when trying to run at my good-weather pace. I imagine I'll build up to it naturally as training continues and I add tempo workouts in.
This is a rest week, meaning I have only 3 running days (instead of 4), and my long-run mileage goes down. Gotta love these little recouping breaks!