i would probally go with the 3.92 with the 410, your truck doesnt really make enough hp to do any towing aside from an atv or two, but the 392 will give a little better mileage, but you will be running a noticeablely higher rpm rang when on the highway.

 

Not that high.

At 70mph with 4.10 = 2308.5 RPMs on 6th gear .79:1
At 70mph with 3.92 = 2207.2 RPMs on 6th gear .79:1

 

I am going to hang on to my used 4.10 gears
but I have since seen other used sets at very modest prices
($25) at the swap meets at Rockingham NC and Clay City KY.

The internet myth that higher diff gear gives better MPG
"because the engine does not work as hard"
won't go away
but the Chrysler engineers who test nearly identical Ram trucks
in 'convoys' around MI and Death Valley
never find that the 4.56 gears in the Power Wagon
give either better city/hw or towing MPG
compared to 4.10, 3.92 or 3.55

ex-Chrysler vice president Bob Lutz is now head of GM pickups
and he recently lowered their diff ratio from the old 3.73
to a new 3.42 to improve MPG on the Silverado/Sierra

Perhaps the false information would not be repeated as often
if more gasoline Ram owners fitted GearVendors units to their
trucks and could see the differences with a flip of a button.

There is a very interesting SAE paper where they took two
Laycock overdrive units (smaller version of GearVendors)
in series behind a four speed manual transmission
and did MPG tests out the whazoo.

You can also go do a test drive in a vehicle with a
Continuously Variable Transmission
like the Dodge Nitro/Jeep Caliber or Nissan Murano
and watch how it handles the gear ratios.

 

But Hank, will I move better from a dead stop?

 

Yes Lowwer rear end gear will make you get off the line better (MORE BOTTEM END) you be winding up the motor faster, and the motor will not be so Lazy but you can lose some MPG up on the HWY then again if you foot is in the gas most of the time trying to keep up 70 MPH in 5th or 6th gear mite as well go to a lower gear you will need put you'r foot though the floor less to keep the truck travleing at the same speed and LESS DOWN SHIFTING onhills and head winds.

I also 2nd they sould never put 3.21 in a full size pickup with a V-6 not enought motor to pull it but on the window sticker and what MPG they were showing it was a good idea at the time, I guess in prefect conditionsNO WindNO Hills or all down hills every where you go V-6 with 3.21 would work fine Ha Ha.

Oh yea if you do go with a lower rear end gear the idea is put you more in the meat of the power band.

 

Lugging the engine will give you worse mileage and be much harder on your engine than having it rev a little higher. There are many people on this site that have gone from 3.xx to 4.xx gears and say they have noticed mileage increases in the city and some on the highway (as long as you keep your foot off the gas).

It's your choice who you want to believe, either the engineers, or guys who have made changes and noticed the results first hand. Either way it's a leap of faith. And you can take all the formula's and numbers and crunch them all you want, but just because it works on paper doesn't mean it works the same way in the real world. All you're going to get here are opinions, and you'll get get facts that support every different opinion too.

My opinion, from personal experience, I'll trust the average guy who tinkers and has done changes over an engineer every time.

 

I hope those who have swapped gears and reported differences remembered to change the speedo gear or their new info is incorrect....

 

I thought that was automatic.

 

On most newer Cars and Trucks use a tone ring off the diff cairrer now a days instead of the old gear to the trany for speedo readings.

Tone ring counts the rotation of the Axle to give you'r readings if you take a look at you rear end case you see a plug hanging from it thats you'r pick up which in turns counts thetone ring roration.
Not how many times the drive shaft turns like old type speedo gears in the trans.

So you can change the Ring and Pinion all day any ratio you want it should not effect you'r speedo readings BUT if you change you over all tire size O/D this will change you'r Speedo readings They make aftermarket boxs that fixs that or you can go to the Steelers Ship and have them recal you'r Speedo for about $110.00 you can buy a recal box for less and do it you'r self.

 

...I have 4.56's and my mileage has gon up considerably...less strain on motor and drivetrain....at speeds higher than 75 do i see a dropoff...but most of my driving is city anyways...