to the forum and to toyhauling. As you've already found, that's one heavy trailer and a "tough pull" for a gas engine. One way you can improve your fuel mileage is to plan all your towing to be downhill with a tail wind <wink> but if that's a tough thing to do, maybe look at improving your rear axle ratio ??? No idea what you have currently, but would guess it's in the 3.55 to 3.73 range. Possibly changing to 4.10 to 4.55 or so gearing would improve your performance. But, doing that may cost more than trading for a better equipped truck that already is set up for your towing needs.
As a current "light duty tower" I'm out of the loop with RV's as heavy as yours, but in "days past" about the only way I'd tackle a trailer that heavy would be with a diesel.
Anyway, welcome to the forum and I'm sure other members will be offering their observations and recommendations.