When I bought my truck, I never thought to check. But is there an easy way to find out what type of diff. I have.?? 3.55, 3.92.........??

 

Look on your truck's msrp sticker sheet , if not got o the dodge web site and put your 17 digit i.d. # in

 

KOr climb under your truck and look on your diff, I know I found mine on the front diff on a tag if it's 4x4

 

a simple way is to look at the RPMs while on the highway. Using the gear select, set the transmission to 1:1 gear (4th gear) - no OD.

For 265-70R17 tires use this gear ratio for 60 MPH
2050 RPM = 3.21 Gears
2265 RPM = 3.55
2490 RPM = 3.92

for the 275-60R20 tires
1980 RPM = 3.21
2190 RPM = 3.55
2400 RPM = 3.92

 

Mine is printed on the axle tag on right side if rear and on front diff cover.