2003 Dodge Ram 1500 5.9 Magnum 4x4. I have been thumbing through the treads trying to find the best ratio, speed and rpm for my 46RE tranny and 35in mud tires. Right now i have a 3.92 in it for gears and at 70mph on the highway i run 2000 rpm. Now i cant remember what Rpm i was running with stock tires, so i dont know what Rpm would be better for it on highway and in town on streets. I have played wth it driving to work on the highway by turning the OD off and see how it runs 1000Rpm higher so 70 Mph is 3000Rpm, and it seems to drive better and has the power im missing but like i said i dont know what my engine should run Rpm wise. I drive probably 30% Highway and 70% Town but also drive to the coast quiet often which is 3 hrs or 7 hrs depending on where i go. Thanks ahead of time

 

One more thing was that i have been looking at putting 4.56 gears in if yall confirm i wont be tached out but i have heard that grinding the pin is need or something. I want to know if its anything special to install these in the front and rear.

 

Did you reprogram you PCM for the larger tires? A calculate 2050 RPM for 3.92 with stock tires. I would think you should be around 1800 RPM with 35"

 

If you're running 35's with a 46RE, you're going to want 4.56's down the road since that would put you closer to stock. Granted, 3.92 is much better than the 3.55 most have.

 

I did'nt reprogram the pcm or anything, my truck was completely stock when i bought it. Everyone i talk to says the same thing about the Rpm and speed. Thats why i asked you all to see if yall had a clue about it.

 

The gears are 1st 2.74 2nd 1.54 3rd 1.00 4th 0.69

 

According to the 2003 FSM, 1st 2.45 2nd 1.45 3rd 1.00 4th 0.69 Rev. 2.21.

 

Cool the place i found that was probably wrong them, and thinking about it if my speedo is off by 3MPH which i found from GPS but say i slow down to 67 Mph and my tach still reads 2000 then what?I never gave thought to the speed being off and changing my Rpms. The only problems i really have are my take offs and while driving down the highway i have no exceleration and it wont keep speed at all.

 

Ok so i checked my Speed and Rpm on the the way home from work and my truck runs 1900-1950 RPM at 70 MPH

 

That seems about right. Maybe a tad high, but that's because I am used to dealing with 3.55's, not 3.92's.