OFF-ROAD's HD Dodge tow/chase truck was in need of a gearing change due to an increase in tire size. Having the 6-speed manual transmission has enabled us to put off this upgrade for a while due to its extremely low first gear, but we were starting to miss our granny gear off road. The problem was that it's not every shop out there that has gears for the newer AAM axles found under 2003-to-current Dodge Ram 2500s and 3500s. Gears for these newer axles have proven to be tricky to get aftermarket replacements for, but we found a shop that has any gear option we could want: JT's Parts & Accessories has AAM axle gears from 3.42:1 to 4.88:1 ratios. The solution was to change out our 3.73 gears for some 4.10s we got from JT's. This may seem like a (numerically) low jump to make since 4.10s come standard in the automatic trucks, but 3.73s are what you get with the manual tranny Combined with 37-inch tires, the 4.10 gears would bring our effective gearing to about the same as from the factory.
Another issue we were having with the truck was that the rear factory limit slip differential had clearly been worn into an open differential. The torque from the modified diesel engine would easily spin the inside rear tire when accelerating and turning at low speeds. We didn't want a selectable locker because that would give us the options of being fully locked, or completely open - neither of which we wanted to drive with on the road. What we wanted is a limited slip differential, but one that wouldn't wear out.
Luckily there is another option for us - an option with helical gears instead of clutch packs. Eaton's heavy duty Truetrac limited slip is now being produced for the giant 11.5-inch AAM rear Dodge axle. The Truetrac uses gears instead of clutches to minimize wheel spin. Using a gear design eliminates the wear issues associated with clutches found in conventional limited slip diffs. This means that it will remain consistently effective over its entire life and the axle fluid will not be contaminated by the shedding clutch material. Once we had obtained the gears and master install sets from JT's Parts & Accessories and picked up our Eaton differential, we headed down to our local 4 Wheel Parts shop to have the installation completed. Unless you're experienced with gears installations, we'd highly recommend taking a newer truck like this to a shop like 4 Wheel Parts that has done countless gear swaps.