do know that the common belief is that these axles really have no need for 140 weight oil. Plenty of heavier vehicles doing just fine on 90. there is some speculation that chrysler calls for 140 weight to make up for the occassional manufacturing defect. While these axles do not have a high rate of failure, they are still known to have some, mostly associated with pinion-related issues-- seals, noise.
all of this is speculation--- but 90% of the info on this board is based on personal experience and not hard engineering studies. ymmv.