SUV's are heavier and have a lot more wind resistance and driveline drag, especially 4x4's. It is what it is. There is no magic remedy to get 27 mpg other than buying a brand new EcoBoost Explorer.
My Polaris has a water leak around the exhaust manifold.....
Best bang for the buck is a cat-back exhaust if you don't mind the noise. Intakes don't make much difference because the stocker is pretty good as is. Just yank the silencer, get a K&N drop-in, and call it good. Same with headers, JBA is the only company that makes them, they cost over $600, and improvement is marginal because the stock manifolds aren't that bad. A lot of guys like the tuners but they cost $400, it will be a while until I save that on gas, so I don't bother.
Keep it in tune, change the filters etc, tranny flush, change the t-case lube (it takes ATF, I use Mobil 1 ATF), it is easy to do yourself if you get a suction gun to fill it with. Axles, the front can only be changed with a suction machine at the Qwicky-Lube, the rear either by yourself and take the cover off or have the Qwicky-Lube do it too. I had the axles done on my daughter's Jeep and the first thing I noticed afterward was that the tranny upshifted much faster, so God only knows what kind of sludge was in the axles.