I had 3.92's behind 2004 Ram 1500 with Hemi and the auto transmission.
Destroyed those gears, went to the original 3.55 gears and lost serious fuel mileage. I'm now debating on going back to the 3.92's again but would like to know if anyone who has gone to 4.10's and what was the resulting fuel mileage. Truck is running stock height tires on 17" wheels.
Anybody? The 3.55's have to go!

 

I'm sure the 4:10 guys will chime in but if you want some 3.92 gears check here

Also, you got 4x4 or 4x2?

 

4.10s will get you better mileage in town, and you will tow A LOT better, and your acceleration will be A LOT better. the only thing that will suffer slightly is freeway mileage. in this case though, id say the pros heavily outweigh the one con.

 

Pilotdriver, I recently changed from 3:55 open rearend to 4:10 DTT. My truck has always gotten pretty good mileage. With the 3:55 I got mostly 16-17 mpg highway running. The 4:10's are really all around much better gear. Lots of fun. and I'm getting 15-16 mpg and I have been running it hard. Blasting around the back roads and doing data logging. If I every settle down and drive it normal again I fully expect to get better mileage than with the 3:55's. My tires are 30.25 inches tall which I believe are just short of the stock 17" tire. I am turning 1825 rpm at 60 mph. Adjusted to th local radar signs. If you have any further questions, give me a holler. Good luck...

 

my truck is a 4x2, with a shell and always a light load in the bed. Mileage was 17 and better with the 3.92's now 12.5 to 15 with 3.55's.

 

Also do I need to flash the computer to change the power curve for new gears?

 

I don't think that is necessary, but I redoot everytime I make a mod just to clear memory to get started again.

 

im running 4:10's but i dont think i can comment as my truck weaight twice as yours , but i will say great low end and towing is a brease

 

4.10s will give the best balance of power and fuel economy with tires up to 33", anything larger and 4.56s.

You do NOT have to flash the computer and if staying with the same diameter tire, your speedo will be correct as Rams read the speed off the ring...

 

Thanks for the input guys, the majority of my driving is highway or at least highway speeds. Anyone that runs the 4.10's behind the hemi, what kind of mileage are you getting?