I had an OK 6-mile run today

I ran 6 miles on the Jordan River Parkway this afternoon. My body felt really sluggish during the run. I jogged/walked the first three miles to warm up, and then I ran the three miles back to my car. The shade temperature was 30 (F) when I left home, and the sun temperature, I would guess, was in the mid 30s. Some days I warm up after just a half mile, and other days I need two or three miles to warm up. My wakeup HR was 55, 10% above my normal of 50.