My wife went with me to the Jordan River Parkway, and she walked the north-bound segment (1.5 miles round trip) while I ran 3.25 miles round trip on the south-bound segment. We were out earlier, and the temperature was relatively cool (mid 70s (F) when we left home and 82 when we returned). The sun was behind a cloud for the first half mile, and it seemed like I was in heaven. The sun came out for the rest of the run, but there was quite a lot of shade due to the early time that we were out (I started running at 8:20).
I got pretty tired during the last half mile. Night before last I didn't sleep very well and only had about 5 hours sleep, including two naps during the day. I did better last night and got about 6 1/2 hours sleep, but it takes several days for my body to respond to having more sleep. Seven hours is my "normal", so 6 1/2 isn't bad.
I did take an extra bottle of water, and it was nice to have the water. On about half the walks, I took a swallow every walk instead of every other walk. Four bottles should be good up to 4 miles, and then I'll add a fifth bottle that will take me up to 5 miles. By then it will be Fall and I won't need as much water.