I was thinking of the Hemi engine when I was talking about the 4.56's.
If it's easier to push the "flying brick", as I love to call my Hemi, around at city/urban speeds typically 60-75mph, then I (in theory) and a few others who have actually done the 4.56 swap, do see mileage increases.
Hemi's going from 3.55's to 4.56's usually only increase revs by approx 300rpm at 60mph. However, the engine is working less hard to push the truck around therefore better mpg.
I was thinking of the swap myself until I got LPG.
Many Hemi owners of the 1500 series trucks report fantastic acceleration better fuel economy and the next best mod to a superchips money can buy when they did the swap?

 

the 1500's get stock 3.55's and 3.92's. the 2/3500's have 3.73's and 4.10's. the power wagon gets stock 4.56 and I think the 4.56 rear end is an option for the 1500's.

I can see where the 4.56 will increase the fuel mileage in that the engine is not having to work as hard due to the engine turning more RPM's. however to turn those RPM's you need more fuel so you have a double edged sword there. I know for fact between the 3.73's and 4.10's of the 2/3500's the 3.73's give you about 3 more mpg. but with the 2/3500's and the 1500's this is the difference between the gassers and the diesel and since the cummins has massive torque down low the RPM's dont need to be to high to get good mileage.

 

I agree with you about the Cummins.........gobs of low down power and torque so better fuel economy.
The Hemi's ......well that's another question altogeather.
I guess that's why I believe they don't offer the MDS in the Megacabs. It wouldn't work. The darn thing would never engage into 4cyl mode pushing all that weight around.

 

Mass plus the aerodynamics of a giant brick, constrained by the laws of physics equals the mileage you're getting. Hence, if none of these change significantly, mileage won't either. What were you thinking when you bought it?

Pony up at the pump, park it, bicycle, or get a hybrid.

 

I'm pretty positive that is just the opposite, bigger tires = decreased mpg.... Larger tires are just that - larger, doesn't it take more power to push them?

 

Over all weight of tire and rim will make a difference of MPG.

 

I have a 2WD QC Hemi too. I am averaging between 15 and 15.5 mpg each week and on long trips I average about 18.5 mpg doing 75mph. I drive at least 400 miles a week (350 just to work and back) and I live in Atlanta with a steady mix of highway and stop and go traffic. If you are really getting that bad of gas mileage then I would suggest two things. First, try changing your driving habits. I rarely ever let the accelerator top 2500 rpm. (Do have some fun on occasion though) If you are driving around hitting that gas alot, weaving in traffic on the highway, and pulling 3500+ rpm from lights then you are wasting gas. This truck accelerates at a normal, easy pace between 2000 and 2500 rpm. Second, if you are driving it mildly then take it in to the dealership and complain. There may be something mechanically wrong with it. Usually one of the first signs of something in the engine being out of wack is poor gas mileage.

PS. Don't trust the computer they are often inaccurate. Go fill your truck up full of gas. Drive it until at least the fuel light comes on. THen go fill it up full again. Then divide the miles you have driven since the last fill up by how many gallons you put in.

 

the truck is fine, but the problem is that i dont drive far at all. u drive 400 miles a week but i dont even drive 100. I drive about 15 miles a day and its all stoplight to stoplight, thats about 75 just to school so its the distance i drive. I work for an insurance company and when i work for them i end up driving about 400 miles a week during off time, and i end up averaging the same as you. It's just that i dont drive far at all. On long hauls though, its a great truck....god i love Dodge.

 

Before I bought my Mega, I test drove both the Cummins and Hemi. True the Cummins has more power and what I really liked is the 100k standard warranty. I tow a travel trailer. The Hemi doesnt perform bad at all. The only difference I see is starting out from a stop. It takes a little more time to get up there ... but the highway behavior is almost identical. True he Cummins would have most likely performed better, but by no means is the Hemi incapable of handling he load.

 

sumncguy, That exactly what I did. I test drove both. I like the quickness of the gas HEMI and I dont pull anything heavy enough or often enough to live with a diesel. Another issue for me was, I go way back in the sticks during hunting season and finding a diesel station would be a problem.