how can i find out what gears and tranny are in my truck? w/o opening the diffs, is there something in the vin# or????? my truck is a 03 2500 cummins,short box, automatic

 

Speed at 1800 RPM?

 

i wanting to say at 65 mph the tach says 2200,maybe 2000

 

4:10's. Mine is at 65 at 1800 RPM.

 

yeah sounds like 410's look in the glove box i think mine said what gears i have

 

cool those are good gears for pulling

 

Hmmm. My speed at 65 = 2000 RPM and I have 4:10s.

 

With 4.10's, 31.6" tires @65 MPH=1955 RPM.
Here is a neat little RPM calculator for you. Use .69 for transmission final gear ratio on a 48RE auto.
http://www.csgnetwork.com/multirpmcalc.html

 

I believe the final gear for a NV5600 is .73. Do not know what the other 6 speed manual final gear is though.

 

I have stock tire (265's), I have 3:73's. At 1800 RPM I'm at 65 MPH.

 

Did you try the little calculator above? Stock tires =~31.6" x 3.73 x 65MPH and .69 = 1779 RPM from the calculator. So that is real close.

 

Thanks for the formula.

 

i have 315 17s wa 9 in wheel, level kit,

 

If you are going to use speed and RPM to tell ratio, the first question is--Have you corrected the speedometer for the larger tire size? If not, the calculations are somewhat irrelevant. Assuming you have, 315/70/17 BFG are ~34.4", 48RE auto tranny (.69),at 65MPH, with 3.73 = 1634 RPM, with 4.10 = 1796 RPM. If you have not corrected the speedo, these RPM's would be fairly close at 60 MPH shown on the (uncorrected)speedo for each ratio respectively.

 

ive corrected the speedo