Well, first, there's a 10% difference in the ratio. This would make your engine and transmission turn 10% faster to get the same speed. As far as acceleration goes, that would be like giving yourself 10% more power. Who wouldn't want that? But the key is like the cummins man said, find where your torque curve starts to flatten out and that's exactly where your engine is it's most efficient.
On my old 440, I was using crappy 2.49 gears and I would get terrible mileage at 55mph but driving at 70mph, I GAINED 4mpg's. Because that's where the 4barrel secondaries would open up a bit and the engine would be into it's high part of the torque curve and running more efficient. A 3.92:1 rear end would have been perfect for this car's cruising. So, I saved on gas, but paid it back out in tickets. It would have been worth the gear change.

 

Keep in mind when you are considering gears that it is MUCH cheaper to get a deeper set (numerically higher) from the get go, than it is to try and re-gear afterwards.

A gear swap on most trucks will run somewhere in this neighborhood:

Gear set: $150 - 200
Install Kit: $100 - 200 (depends on the level of the kit)
Labor: $300 - 600 PER AXLE

So, on a 2wd you'd be looking at $550 - 1000 and $1100 - 2000 to regear a 4wd.

Start adding in lockers, LSD's, etc and that only tacks onto the price.

A wise man once said, "Swapping gears for fuel economy is like ordering a Diet Coke with a Whopper meal." It just doesn't pay off. $550 will buy a lot of gas......$2000 will buy a lot more gas, so consider wisely.

 

I am running 3.73 and tow a large bass boat all the time in the summer with out breaking a sweat. I think the key is the tire size. Dogde is smart enough to only offer 17" wheels in the 2500-3500 HD trucks.Make sure you get the lighterand strongerpolished forged wheels if you can.

 

The size / weight of your wheels and tires is only part of the equation. Mostly this affects hard, fast acceleration.

Tire diameter has a greater affect on towing performance.

Going to larger diameter tire has the same effect as putting in higher gears (numerically lower). Guys that have the 17" wheels have about a 31.5" tire diameter. Guys with the 20" wheel / tire combo have about a 33" tire. For both trucks to perform the same, the guy with 33's would need 4.10 gears and the guy with 31.5's would need 3.73's with everything else being equal.

If both trucks had the same gears sets, the guy with 31.5's would accelerate and tow easier.

 

4.10's with 33" tires for sure, even with a stick.

Actually the auto-trans would handle the 3.73 ratio better because the converter multiplies torque.

 

Well, my 20's have the lower profile rubber from the factory which was swapped to 285/50R20 and they are the same exact diameter (measured 31.5" if I remember right) as my 275/70R17's. So my speedo isn't out of whack one bit. I went for the 17 inch steel rims for winter just because the 17" tires are about half the price of the 20's which more than paid for the rims, and slightly narrower for deeper snow.
It never seemed to change my mileage having the heavier steel wheels, just not as fun to drive.

 

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4.10's all the way