Most of the above. An aftermarket intake won't do that much for you, and you can modify the stock setup to be as good as any aftermarket CAI. With that poor mileage, I'd for sure be looking at the O2's, MAP Sensor, and spark plugs. The biggest weak spot on any of the WK's is the exhaust system. With my mods. (see signature), my Hemi routinely gets over 20 mpg highway....usually ~21-23, with a best of 24.4 mpg.
I just got back from a 1786.6 mile trip and overall average for the whole trip was 20.65 mpg......86.48 gallons of fuel. It would have been better if I had driven my normal 65 mph in 4th gear instead of 65-80 mph in 4th and 5th. That included almost all mountain driving, head winds, two climbs to over 6500 ft. and one to 7800 ft., and about 40 miles of city driving. Altitudes ranged from ~500-7800 ft. elevation. I use 91 fuel at lower altitudes and climbing, and 85-87 at higher altitudes. I find that using Standard/Chevron fuel works the best and if I can't get it, I add about 6-8 oz. of Techron. The very best fuel I've found is a Commerical Fueling Network (CFN) station in Wells, Nevada. It's a "no name" fuel, but all of my best mileage has come from the same pumps at this station. I use their 85 fuel, as the elevation there is 5500+ ft.
The bottom line goal to improving fuel economy is to improve the Volumetric Efficiency (VE) of the engine, without going too far overboard. IMO, your first order of business (aside from making sure all engine tune items are working properly) is to fix the exhaust. Again, IMO, headers and a low restriction header back exhaust system is the most important thing you can do. I had to have my headers custom built about 3 1/2 years ago, and they've easily paid for themselves. Next, you may want to consider advancing the stock cams by about 5-10 degrees. I have advanced aftermarket cams in both my Hemi vehicles, with a 6* advance on the WK and a 10* advance on my LX. It gets 27-29 mpg highway with about the same mods. as the WK. A Superchips Tuner with the Advanced Transmission Tuning Application (ATT) will allow you to set your shift schedules to keep your engine RPM in a range that is closer to your torque curve. That's why I drive mine, most of the time, in 4th gear....usually 65 mph in 4th gear, ~2400 RPM. If I could up the RPM to ~2600-2700 RPM, I am sure the mileage would go up a little more. Other things you can do is to cut weight (hard to do), and try to improve the aerodynamics a little. I added an SRT body kit (drag coefficient of .39 vs. the stock Cd of .41) and lower it a little which further reduces the Cd. I also use Airtab Vortex Generators on both my vehicles. The weight of mine, loaded for travel, a full tank of gas and the wife and I in it, runs right at 5500 lbs.
Other little things you can do (after the above) that make slight differences (improvements may be slight, but cumulatively they all add up) are add an underdrive crank pulley, higher voltage coils, improved, modified stock intake (two air inlets into airbox and low restriction air filter), slightly larger throttle body, and a resistor in line with the IAT Sensor to fool the PCM into thinking intake air is cooler than it really is. I haven't done this to my WK yet, but I have an adjustable setup on my LX which may help a little. Theory is that cooler intake temp. will allow the PCM to add a little more timing advance.
A few other obvious things are front end alignment (I have mine aligned with the wife and I sitting in the vehicle), proper tire pressures (go on the high side), making sure the wear patterns encompass the full tread width. Too high pressure wears center only, too low wears outer edges only. Also, much above 65 mph your fuel economy starts tanking. If I drive 75-80 mph, I'll lose 1-2 mpg. I also use cruise control as much as possible which, along with the Superchips ATT App., maximizes the MDS "on" time of the Hemi.
Good luck, and have fun tinkering. For me, fuel economy improvement is a game. It's fun to see what works and what doesn't. My goal for the WK is a fairly consistent 24-25 mpg. I've got a few more ideas I'll have to try though.