Fun but Tough 20 miler

So yesterday was the first of two 20 mile training runs for Madision Marathon. It was tough. Towards the end it was 60 degrees and sunny aka perfect weather. Not perfect for me. I'm trying to prepare for the hot weather I over dressed to simulate hot weather.
I was trying to have gels every 4 miles.
I was running at Busse woods and there happened to be a half marathon going on so I jumped it. I ran with random people and struck up conversations. Everything was going great until I hit mile 11. I was having wardrobe malfunctions, my stomach was starting to feel woozy, and my legs we're getting heavy. Looking at my garmin I was running at 8 minutes per mile at some moments. In summery I was going to fast, was overheated, had too much Gatorade and too much PowerBar gels.
After my 3:20:00 run I must of slipped in my car for a hour until I got a phone call from my second job telling me to come in.
In two weeks I have to:

Not go out to fast at the start

Get peanut butter gels

Know ahead by how much water to replace every hour by watching my water loss