I want to know what pple have done to get the best millage out of a 4:10 geared CR with the 6speed. Im getting around 15mpg average, this is highway and town driving mix. Lets hear some ideals and facts!

 

I don't think there's much you can do to get good mileage out of a G56 with 4.10s. IIRC, they have a slightly lower overall gear and combined with the 4.10 you must be over 2k RPM at 65mph, even with 35" tires. I think I heard somewhere they increased the final OD ratio at some point but forget what year that happened and it was still lower than the 48RE, IIRC.

 

It depends on what your running. If you have 4.10 gears and want gas milage you should go 37" tires or bigger to balance out the RPM's. I have 3.73 gears with a Smarty POD S-06 and I am currently getting 23mpg combined highway and city driving with my 6 speed.

 

I take that back, im sure the 03s are good, but if your looking for one might as well find the 600 engine. I would say and auto would be fine if your not worried about putting money into it, or plan on keeping it stock. Im an old sole, and love the mechanical 12valve its a great engine sounds awesome looks awesome and is a power house. If you want a new truck, don't heasatate get a new CR. but just keep your 12valve dont sell it lik i did

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I have the nv5600 not the newer G56. Maybe i will lookinto changing the gearation to something higher?

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how big a lift do i need to tuck 37x12.5/17 or maybe a inch or 2 skinnyer

 

If you want any mileage out of 4.10's & 6 speed, you have to lower your rpms (bigger tires). Mine is an 04.5, HO, 6 speed, 4.10 truck. Stock tires I was turning about 2700rpm @ 70mph. With 315's I'm around 2100rpm @ 70mph. I never hand calculated but the overhead (I know they aren't real world) would read a consistant 20.8mpg on trips to Indy. Never have checked since adding a Programmer, boost fooler and CAI. Pretty much anything over 2000rpm your burning a lot more fuel.

 

Highway i get around 14-15, 9-11 city with my early 04 3500, 4:10 auto. Also about the RPMs, @ 70 the RPMs are just under/around 2k depending on the road of course

 

The problem with lift and bigger tires is it is generally a wash, even loses mileage in some cases depending on the combo. Bigger tires are heavier, more rolling resistance and the lift increases drag. When I went to just 2" bigger tires (same lift / 34" tire) on my 1sGen I lost about 1MPG across the board. When I went to 35s on the '07 (same lift 2" bigger) it was a wash, basically same MPG pushing the bigger tires. I don't believe anybody who claims over 20MPG running 37s. BS, IMHO.

Straight highway, babying it at 60mpg on flat ground, maybe. But that's going to be a rare exception to most normal driving.

 

Running a smarty JR, FASS, and straight exhaust; I average around 20 to 21 mpg cruising around 60mph towing around 1500 pounds of trailer. The high cruising RPM is your problem, you can only push a brick through the air so many ways. I have done a personal best of 26mpg (all hand calculated, several consecutive tanks) across North Dakota, and that was before the Smarty Jr.

I have the exact drivetrain you describe...you just can't be in a hurry to get anywhere.

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I ran a set of 315x70r17 BFG AT/KOs for about 10k miles, and got some of the best mileages running them...it drops your RPM down significantly (assuming you are willing to drive the same speed). If I could get out from under this 5vr, I'd be running 35s again.

 

With the 6-speed and 4.10's, about the only thing you can do without changing the hard parts is slow down. If this isn't an option, be prepared to get your money out. Some people try taller tires. Problem is, taller tires usually equal heavier tires, or at least wider tires, and either will cancel out ANY gain you get in MPG's from the height increase and many times, the resulting mileage will actually be worse. (my 33 x 12.50's cost me on average of 2.5 mpg's over the stockers)

Next up is changing the axle gears. You can now get ring and pinion sets as high as 3.42:1 for the 3rd gens. This is fine if you aren't towing at or near your max CGVWR, but throw a heavy trailer on and you'll cuss the day you made the swap... especially if you've done any real towing with your 4.10's.

Another option (and the one I'm considering) is installing a Gear Vendors Overdrive unit Gear Vendors Under/Overdrive Dodge/Dodge RAM Manual transmissions.. They bolt in place of the transmission (or t-case) tail housing. Are hell for stout and allow you to "split" the gears plus give you a second O.D. Gear Vendors say a modern diesel truck should expect at least a 20% increase in fuel economy. The down sides are they are expensive (MSRP is $3500.00) and can only be used in 2-wd, although it's not likely you'll be needing 4-wd and double overdrive at the same time!

 

I run a GV on the 1st Gen and love it. Like I said before, I lost ~1MPG overall with the 34" tires on that truck, but that's due mostly to the mixed driving I do. Alot of fuel goes out the tailpipe shifting up through the gears in city traffic, which I estimate amounts about 30% of my run time. I haven't had it on a long enough trip yet to get an accurate highway mileage number with the GV, but I'll bet it's well into the 20's straight highway - with 4.10 gears.