Describe your race day.
I think both 2016 and 2017 races were lucky in terms of weather. We finished in about low/mid 60s and sunny, but it's actually more common for the weather to be 10 degrees warmer.
I did quite a bit of research on this race ahead of time, and I thought I would gain a 15-20 minute advantage over an equivalent flat. fivethirtyeight's marathon predictor estimated that for a flat marathon I would have been able to run a 3:19, which I thought would translate to between 3:00 or 3:05 on this course, but I ended up running a 3:11. I believe 2017's course change slowed it down some compared to 2016, but 2017 had a strong tailwind for the last couple miles.
I think based on my faulty assumption on how much this race would give me, I went out a bit too hard. Breathing didn't seem very labored, but heart rate was higher than what the effort felt like. While the decline gave me speed, the elevation took away some, though definitely not as much as I got from the decline.
Once I got to mile 23 and had to go out and back against the wind, my wheels pretty much fell off. Heart rate would not go down at what I usually consider a very easy pace but I never stopped running.