I found a way to do a simple differential - this may be interesting in doing a better script for trucks and off-road vehicles. Basic is, i dont have to include it in the computation of the "force" that is applied to the wheel, but make an addition to that. As OT has a way to get individual wheel RPMs, ya make just a set of difference variables between the two at an axle and multiply the "force" by it at each proper wheel. adding an constant to the difference variables can be used as an tuning of the differentials ratio.
... in addition, an binding-key controlled variable is included witch says if the differential lock is on or off, making the addition be equal to the computed number, or 1 (as the differential being locked, thus giving all wheels the same force)
Doe, when a wheel gets off ground, the force at an differential-driven axle goes entirely to the wheel white less resistance (the one in the air). So there is also an script witch looks into the height of the wheel and if one of them goes off, it renders the other force-less - giving the negative effect of the axle differential to effect.
(off course, you must use the "log" script to first find the minimum position of the wheel (when it just hangs in the air) manually, cause its a different number to the minimum in the wheel-parameters as it takes a few more stuff into accout)
Off course, using it on an basic setup of wheels (where the wheel in script is also having the mesh) is not good, as all wheels getting off ground stop rotating in the basic OT script way. So for showing it off at a graphical level, the mesh of the wheel should be a separate one with rotation projected thanks to the ".rotation " value of the actual script wheel. Witch, when going off ground, will switch to an rotation based on intensity of the gas pedal (and maybe even the gear selected, so its different at different gears and stops or reverses at neutral and reverse gear positions).
.. and also rotate the both wheels on the axle the same angle-speed if the differential lock is engaged (cause the basic OT way it turns due to the ground).
... will do some testing with some details and try to paste-bin it for ya. If ya have some idea of pimping it up a little more, let me know !