So If I am reading between your lines correctly you've only slowed down a bit further :?: No higher tire psi, cardboard radiator block or hot air intake modification :?:
You should be able to maintain MPG by _slightly_ accelerating back down the hills to regain some of the lost speed up. Just watch the MPG indicator and keep it HIGH :!:

And when traffic allows, increase the intensity of the rollercoaster ride to further increase MPG without any more time spent :!:

(slow a tad bit more on the uphills and regain it bcak on the downside.)
HTH!
