I didn't read your original post so I'm not sure if you have a 4x4 or the 4x2. If you've got the 4x4 you simply won't get the mileage that us 4x2 owners get. Different gear ratios and more moving parts (friction) will lower your mileage. But even so, the advice given above will help. The thing about the Patriot is that it wasn't intended for flat out acceleration so if you're looking for a good green-light punch, you're not going to get it.
Do you have a manual or the CVT automatic? I've got the CVT in mine and it takes a while to learn the power curve. If I stomp the pedal to the floor, it bogs down... BUT if I stomp it HALFWAY down, I can chirp the tires and it launches from a stop. Not Corvette acceleration, but pretty good for a 4-banger powered SUV the shape of a brick.
I just drove about 800-miles around the state on vacation, from 2,000 ft elevation desert up to 8,000 foot pine trees, mostly highway with the a/c on, and with 40mph crosswinds most of the time. I averaged 29.5 mpg and even had it up to 32mpg at one point. I don't think the roof rack cross bars make a bit of difference. I have them and they don't seem to affect anything. I think the windshield pushes the air over the low-slung bars. However, I notice a HUGE difference in highway mileage when I have my bike(s) on the roof. With them up there I usually only get about 24 on the highway.
If your Pat is under 1500 miles, the engine is still breaking in. I saw a significant improvement in mileage after that point. Keep your tires aired up, go easy on the throttle, and try to be as "smooth" in your driving as possible. Anticipate lights so you can decelerate slowly rather than have to slam on the brakes, etc.
Good luck and enjoy the Pat~