I think Cruise Control does help a lot. But it's hard on this highways here to just use Cruise Control. Many people drive too slow, others too fast and lots of people cut you off and the stupid highway is mostly 2 lanes lol

But I'm up to 18.5MPG now just when I think I will do great milage my gas seems to drop like crazy as soon as I do a little of city driving.

It does seem that just on the Highway with Cruise control at over 100KM/Hr It would do pretty good.

I will set all my tires at 39 or 40 PSI on the next tank fill up as well and see how she does. On my last oil change the guys there set them at 34 PSI I believe, the recommended is 36 PSI for my van and the max on the tires says 44 PSI. Now my ride does not feel as smooth as before with 34 PSI

 

So a little real work experience..

Driving the 2008 3.3 GC at 100 or slightly below got me 11L/100K while cruising on the highway.

I have also noticed that from a full tank to half I can get about 380k before half marker...after the halfway mark it drops rapidly. Many time I think I'm gonna get 600k on a tank or more but only reach about 500k and change.

Rule of Thumb to increase MPG.

• keep your RPM under 2K while crusing
• no rapid acceleration
• fight the impluse you would normally have for a coupe or sedan...

It's a GC own the road and cruise like no ones watching.

Lastly...PLEASE honour the unwritten rule..the left most lane on the highway is for passing. The times I WISH I can disable a car and have it push to the shoulder for not respecting this rule or a RAM to bumb them to inform them that they are a hazard to the road.

(RANT OVER)

 

These things are really heavy and have the aerodynamics of a brick. IMHO 11 l/100 km (21 mpg) is respectable.
Our 2012 averages 12.5 l/100 highway and city. The GC gets the same mileage as the 300C with the 5.7 Hemi and this is on the same route. They weigh almost the same. The 300 has a lower drag coefficient and can shut off 4 of 8 cylinders on the highway. It has also acheived 26 mpg on some long highway hauls at 70 mph. It's also an expensive car to pay for the technology.
Regardless, for our GC's, technology goes a long way to set the field for you and I think Chrysler has done a pretty good job of it but the variables like how you drive, where you drive and how well you maintain your van determines the difference between exceptional and mediocre performance/mileage.
You can spend money on programmers (not chips, but real reprogramming) to get better mileage at the expense of power and performance. Expect to pay $650 for a dyno run and custom tune if the interface is available. The result will be a dog with good gas mieage.
Chips, water injection, O2 generators, throttle body spacers and anything that costs less than $500 is a rip off.
So, looking at the above where is the best bang for the buck? You are!!

 

First, forget about kmaxx or whatever devices. If they worked, don't you think one or the other mfr would use them to gain a sales advantage for the resultant mileage advantage? K&N might give a little more horsepower, but only at higher RPM's, and since the engine is turning relatively slowly at normal speeds, you have plenty of airflow with the mfr's system--hence, no gas mileage advantage to aftermarket intake systems. Basically the same is true for opening up the exhaust--it is only effective at high RPM's.
Spark plugs? Stop looking for the magic there. Unless you're getting misfire, you'll see no difference except the extra you'll pay for the fancy plugs. NGK admits as much on their website. I'm not going back to look right now, but if memory serves, they say you MIGHT get a 2% increase if your old plugs are really worn.
The only two answers that work are: Make sure the tires are aired up, and Drive slower and steadier.

 

Technique is everything. Coast when you can, accelerate at a moderate rate, use cruise when able, and stick to 100km/h (60mph) or less. All the gadgets, gizmos, latest and greatest filters and plugs will not have as great an effect on mileage as technique. I had a 98 Windstar with the 3.8L before my 2012 GC, so I am absolutely thrilled by my mileage compared with that beast!

 

Fuel economy on the 3.8L is somewhat dismal and I'm sure the new bodystyle with it's US postal truck body design doesn't help.

Anybody claiming 29MPG at 90 MPH in a minivan is either joking or calculating very wrong. This sort of wild claim is very common. You can't get that sort of economy at 90 MPH from a Neon or Focus with manual tranny, let alone a 6' tall 4400lb van.

I have owned 3 minivans and driven them a total of 400K mi:

My 1992 Ford Aerostar 4.0L with 4WD got between 17 and 20 MPG in suburban driving and got between 19 and 21 MPG on the highway at 60 to 75 MPH. It never got over 21 MPG. It had 3.73 gears with 14" wheels and was all about acceleration, not efficiency. It could suck the headlights out of a 5 liter mustang under 35 MPH, unless they were really on the ball.

My 2001 3.3L Dodge Grand Caravan Sport gets 18 to 20 MPG in the same suburban driving. It gets between 20 to 23 MPG on the highway at 65-75 MPH. The 20MPG figure is around 75 MPG with significant load. One time I followed 53' semi's in their slipstream around 60MPH for a couple hours and got a best of 26 MPG. They sucked me along in their wake and gave me the finger. It won't get better that. The EPA rating was 25 on the highway.

My 2008 GC 3.8 6spd auto SXT gets about 18 MPG in suburban driving. If I keep it under 60 on the highway, it'll get 22 to 23 MPG...but who does that for long?? At 70MPH it's getting about 20 MPG. The fuel economy drops like a rock over 70 MPH.

My 1993 Corvette LT1 350V8 with 6spd manual got 31 MPG at 72MPH which is equal to my daughter's Ford Focus 2.0L 4 cyl manual tranny 2 dr hatchback car. The engine turned around 1400rpm at that speed and it's cg was under 0.30 so it wasn't working at all. The Vette consistently used less fuel than my buddies 944T (4 cyl turbo) on 3+ hr trips to the track. He was amazed.