sorry but slowing down is your best bet, keep it under 70, if you can keep it at 65 you'll see even better mpg.
I've also found that that the AC kills about 2 mpg vs windows up and no AC on road trips. windows down kills about 1 mpg.
only other trick is to draft behind a big truck, our mpg is so bad because of the lack of aerodynamics in the body of the Jeep.
also, if you're wondering, premium fuel wont help.