X2 on Diesel Torque.
The gearing is not the weak point for the CRD, it is the Original Torque Converter when compromised by a soon to go bad front pump. Chrysler cut the torque in the ECM and changed the shift patterns in the TCM with the F-37. This was a cheap @$$ Bean Counter Engineering stunt to avoid replacing the front pumps and using the 0.200" dampener springs in the torque converter that VM recommended from day one. Now Chrysler makes a new pump and sells the J8/Euro as the replacement torque converter.
As long as you take care of the problem with the weak Original Converter/problem front pump, you can address the ECM issue with a tune.
To fix the TCM problem you either need to either pay a bunch of bucks to find a Pre F-37 TCM, pay $1,200 up front for a custom TCM tune from bgchrysler.com, or wait for a TCM flash under development. I am personally involved with a fix for the F-37ed TCM. To use some legal court room BS, the prosecutor has been assigned, former Illinois Governor Rod Blagojevich will be the assigned as the defense attorney (they shurly will loose), but the Jury is still being selected.
So, if you regear the differentials, you will make the F-37 problem worse unless you put on tires that are so big that you cancel out the ratio change, then you will need a serious lift kit.
Fix the weak point with the front pump and Original Torque converter, get a tune with the torque you want, and wait for a performance TCM flash, you will have a stronger rig.