1. If your averaging 13mph you'll gain nothing by moving to a more aero position.
2. Only change your chainrings if you can maintain a pedal cadence of 100 or higher in 3 smallest gears in back while in the big ring in front. If your averaging 13mph there's no mathematical way that a bigger chainring in front wil benefit you.
3. Use a 1.5" or so tire. Narrower isnt always better. I'd put money in the bank that a high quality high TPI count tire in 1.75" will roll better than a crap low TPI count no-name tire in a smaller size.