I have a 2004 ,2500 ,4X4, 5.9 diesel ,4speed auto with 4:10 gears. Most of my driving is interstate 70 to 75 MPH pulling a 14 foot cargo trailer with 2, 4 weelers in it. I get about 10 to 11 MPG pulling the trailer at 70 MPH and 12 to 13 with just the truck at 75 MPH . Thinking of changing to 3:42 gears front and rear Im told with American axel my only options are 342 or 373.Im looking for better fuel milage I just wounder if 342 is to high.

 

quite a jump from 4:10 to 3:42

 

Yeah it is. Also, would the cost of replacing the gears ever make up for the savings in fuel (if any)?

 

I have a 2010 Ram 2500 4x4 and am going to change my gear sets from 3.42 to 3.73. With the 3.42 I am limited to 17,000lb total truck and RV. I only have a 26ft but it weighs 10k and I am wanting a new 28ft Winslow and it will put me over the 17k limit. If you get serious about the change I will have a front and rear set 3.42 to sell. Mike

 

If you are sure you'll never tow over 2000 lbs it may work out but probably won't give you 30 mpg. I would keep the 3:73.