Cut from the FAQ:
============
One reason the Chevy Silverado gets better highway MPG than a Ram is that it has a lowered body drop for better aerodynamics compared to the Ram
and F150. {The Silverado also is not as high, slightly narrower, is about
400 lbs lighter, and has an 5.3V8 with a shorter stroke and 9.9 compression
ratio.}

 

On Tahoe/Suburbans.....take a close look at the 'air vents' at the rear corners of the vehicle. Those little black notches act like vortex generators. If you are ever travelling on a highway through light fog, or on a dusty road you can see this. The funny diagonal bar near the rear window of the Chevy Avalanche is also a vortex controlling device, and was partially copied by Honda on the Ridgeline.

One thing that amazes me.....
There are more than thirty MPG improving modifications listed in the FAQ
but everyone seems to only remember the short section on vortex generators. These same people also forget the warning in that section
that the gains are small, and that one must always admit that without a
$100 million wind tunnel we can only guess where to put them for best effect.

If I had to rank the MPG improvements listed
the vortex generators would not be Number 1
they would be more like Number 20.

 

I can't answer the question of why one truck gets better milage than another but VWandDodge got the closest. There are many factors that determine milage in real world driving. Driver input is one. Not every person drives exactly the same. I have owned 3 GM trucks. A 66 with a 283-V8 when I was 16. Don't know the mpg because gas was .52/gal and I didn't care. A 78 GMC standard cab short bed 2wd that got traded off because it got 8-10mpg (350 with 4bbl) and a 98 Chevy Tahoe that got 20-22 when my wife drove it, and 16-18 when I drove it. Best I ever got in my dodge truck was about 18 and that was when it was brand new. By the time I jacked it up 3", put on bigger tires, messed around with the exhaust added a tool box full of heavy crap, added a receiver hitch, it was down to about 12mpg. I like the stance with a 3" lift so I dropped the size of the tires down from 33" to about 30". I traded mud tire tread for hwy tread. I fixed the little problems that all affect how the engine runs and I regularly get 15-17mpg driving like a sane person. If I get on it a few times, I drop my mpg. I used to bitch and moan about the 55 mph speed limit but when they raised back to 70 and 75 in some places here in Texas I soon found out that driving slower got me better milage. I drive about 65-70 now on the hwy and can maintain decent milage, if I go faster I use more gas. If you truely want better milage but need to keep your truck then the secrete is to get it as low as possible without comprimising ride quality and make it as lite as possible. I have decided that after my trip to the ranch this weekend I am going to empty my tool box and any other uneeded thing I have in the truck. I can always put that stuff back in when I need to. I will just keep my jack and lug wrench but the rest of it has to go until gas prices come down. Jeff.

 

As always Hank I value your input! The Intrepid was a p.o.s. as far as reliability issues. It is near the bottom of all quality and reliability ratings in many tests. The body style had nothing to do with this - the parts in the car were not very reliable - thus people didn't want to buy a p.o.s..
We own a Chrysler 300C with the 5.7 Hemi and all options.It may be un-aerodynamic and heavy - but ours gets 18.6 in town and 25-29 on the highway. My wife loves the car and isn't afraid to mash the gas. We looked at many other high end luxury vehicles that cost a whole lot more than the 300C and we both agreed that if we could afford to buy any car in the world - we would keep our 300C. Because it is a good solid car with a lot of interior room and all the goodies - and it hauls a$$ when you stand on it. It gets better mileage than most other luxury vehicles as well.
I'd be satisfied if my truck got 18 on the highway!

As to the "BS" on 4x4's getting over 18 - here is the list. All these are buddies of mine at work. We all drive 23 or more miles 1 way to work in city/highway conditions. '99 GMC 4x4 reg cab with a 350 - 18.1-19. 2005 Chevy ext cab 4x4 with the 5.3, 18.7-20.2. 2007 Chevy 4x4 ext cab with a v-8 (not positive on exact size) 18.3- 19.7. There are a few more that get over 16.

I am at a loss. I didn't care about mileage when I bought mine, gas was $1.25 gal. If it would stay around $2 I still wouldn't care, except for the idea of it getting so much worse than all my buddies. $3 and higher is starting to hurt. Costs me $65 a week to get to and from work. Doesn't matter if I run my average 70-75 mph or 60. I've tried it both ways.It would make sense to go get a cheap little car to drive - but I already have too many vehicles, and I get claustrophobic sitting lower than everyone else at 70+mph on the highway. Thought about getting a motorcycle - but that would be pretty dangerous riding on the highways I have to take and the amount of idiots on the roads here. I have quite a bit of weight in my toolbox - but I know that just as soon as I take a bunch of it out to save weight - I'll need it and won't have it. [:@][:@][:@]

Again - if any of you have a "reflashed" pcm - let me know what the change in your mileage was. Keep in mind that I have the Hypertech already, so the curve probably wouldn't be as great as the change from a stock truck.