Any stretch of flat after downhill is going to feel rough and any slight uphill it going to feel impossible, so train your brain to handle that and practice downhill to flat or rolling hills. Don't throw your gloves at 3, you will want them later. Additionally, dress warm, it doesn't get sunny until about 16/17 miles in and even then it's still very cool. On the downhills, don't fight it and hold back, that trashes your quads, just let gravity pull you. Relax your breathing on any uphill and don't push too hard up the hill like you would at lower altitude.