Looks like there is a +2mpg advantage on the highway for 4x4/AWD models. A little could be due to transfer case? The Durango has a lower drag coefficient. That's probably the main reason. They have the same tires, and I believe the same gear ratios. Drag has a lot to do with MPG at highway speeds -- especially when driving heavy beasts.
I expect these things are rear wheel drive all the time. 4wheel drive when there is slippage enough to get the transfer case excited.
Even Acura MDX with SHAWD is front wheel drive until the rear wheels are called for.
Nah... QTI and Durango are simple old style open light truck transfer cases. Functionally a open diff in the middle and open diffs on each axle (there is just a little rear bias because of the way the gears are designed). They depend entirely on brake traction control to stop wheel spin. These are what some of us call AWD systems. The complexity of axle disconnects (e.g. slip clutches) are added to other more car like vehicles to save some mpg. These are typically not strong enough for light truck applications, light trucks have more significant things that affect mpg. The mpg improvement of an axle disconnect is probably in the noise.
The QTII, on the other hand, has clutches within the transfer case, so it can run in completely open to completely locked depending on the whims of the traction computer. This is a true 4x4 case.
2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6, 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
They also have the same tires and gear ratios. Thus, any difference has to be in the drag -- in which the Durango has significantly less of. As stated above, drag make a big difference in a 5200 lb beast in speeds of 65 and above.
The window sticker for a 2014 AWD/4WD Hemi Durango rates the mileage at 14 city / 22 highway. The JGC is 14 city / 20 highway.
It's possible that the drag could be the difference, but I'm not sure.
Real world mileage - I've seen 25 mpg according to the EVIC display going 65 mph on a flat road in my 2014 Hemi JGC.
It is puzzling me, last year sticker mpg with 6 speed is still 20mpg highway. Why 8 speed didn't increase the mpg? In ram trucks it did increase 2 mpg on hemi. Same as durango, 8speed increased 2 mpg on sticker.
Most of the time EPA is simply self testing, and occasionally marketing department has a say about it.
By keeping hemi 4wd in 20mpg, the diesel shines even brighter over it. In durango there is no diesel, and in Ram diesel is introduced very recently on 2014 models.