Just wanted to give my opinion on the few things i've done. Swapped gears from a 3:21 to a 4:11. Love the change but wish i would of gone with the 4:56. Put Cooper Zeon 275-60-20's on. LOVE the way it changed the look of the truck! My only complaint is that is seemed to of KILLED my gas milage! Is this normal? Anyone else notice this?
This is my first post, but been on this forum everyday since I bought my first Dodge truck ever! Have always been a loyal Chevy guy but i'm a Dodge convert. I love my truck! I traded in a '09 Silverado ltz with the 6.2 for my Hemi and love it!

 

Pretty sure it was the gears that killed your mileage. I've got 3.92's and my mileage is definitely not as good as my old truck with the 3.55.

 

Tires can affect MPGs, especially ones with more "agressive" tread patterns. The Coopers I would expect some loss over the tame Good Years. And of course as mentioned your gears will also hurt you, more so on the highway.

I would like to hear real world MPGs for the Coopers vs stock rubber. Yours would not be a good example given the gears. I am not going to replace my tires for the sake of looks, but at 35Kish they will go and I do not want the GY again. The Coopers are in play, but would like to know what people loose just by adding them. I am leaning towards the Bridgestone Dueler Revos as I think they would do better with MPGs.

 

Not knowing the original tire size, I assumed it was the stock 26570R17 which is 31.6 inches tall and you went to a 33 inch tire for a 4.4% increase in diameter (4.4% less axle rotations per mile traveled). But the axle change from a 3.21 to a 4.11 is a 23% change ( 23% more pinion rotations per mile traveled).
In a nutshell, your truck is running around 18.6% higher RPMs than before for the same speed. Although not linear completely, I bet you are getting about 20% less MPGs than before.

 

My gears actually helped me big time on my mpgs as I live in the hill country and tow and haul on a regular basis. I changed the gears 6 months ago, I changed the tires 2 weeks ago and again..... it really hurt the mpgs. This is the 3rd truck I have put the EXACT same Cooper tires on and in all 3, it took a big toll which again I dont care b/c I love the way they look and I never by a truck for the mpgs.

 

People will say a lower gear may help your around town driving. I disagree, unless you are really stoplight to stoplight all the time. I had a Chevy Avalanche and went from 3:42's to 4:10's I had 33" tall tires with both gears and lost 1.5mi per gallon overall. I was pissed because I bought into the opinion that my mileage would get better because 90% of my driving was "around town". Really wish my sport could have come with 3:55's with a posi track. This is the only thing I don't like about my truck.

 

When you changed the tires, did you go from 17" rims and tires to 20" rims and tires? If so, you have to get the computer updated with the new tire size or the odometer will not be accurate leading to false MPGs.

 

Cross, you said you live in the Hill Country, as in the Texas Hill Country? If so, where did you get your gears done?

 

MPGs will improve as long as you drive the vehicle int the engines "sweet spot" for the RPMs versus the load. So if the gears helped in towing in hilly areas then you will gain but if you get out in the highway and run at 75 MPH, what MPGs do you get?

I have a 2009 hemi CC with the 3.21 axle. I am hand averaging about 18-19 MPG at 75MPH with some hills. I will start towing my camping trailer (3500 lbs) when the weather improves. After a few trips I may go for a gear change and LSD.

Around town I get about 14 MPG. I do baby it for the most part. When I get the urge to go fast, I drive my '02 vette.

 

when i switched to the cooper zeon ltz 275/60/20 from the stock gy hps
also 275/60/20 it seems that i loss an average of 1-1.5 mpg,not bad considering the more agressive tread,beefier sidewall all around better truck tire.i consider the mpg loss minimal.and ive put approx 12000 miles on my ltz's and couldnt be happier