I know how to do it the old fashion way.
Jack up the truck, mark the drive shaft and the inside of one tire. Then rotate the tire and count the number of tire rotation to the drive shaft. If the the tires rotate 3 3/4 times around then the ration is 3. 73 to one. If the tires rotate a little over 4 times around then this would be 4. 10 gear set.
You did not say if you have an automatic or not. If you have an auto with 3. 73 gears, then in 6 gear at 60 MPH you will be close to 1500 RPMS with LT265/70R17E tires.
Another way is to contact Dodge but I have lost the link, someone may have this and then you can get your build sheet. May take up to a month to get.
Hope this helps.