Sky,
Since you are towing, not TC-ing, it seems to me you made the right decision with the 10K max. It would be interesting to know what the differences to the truck are between the 10K package and the 14K package. My guess is the 14K package has:
larger rear AAM axle spline count and larger ring gear and pinion.
more springs in the main pack and thicker overload spring
more springs in the upper secondary pack
bigger brakes
one more or larger cross member over the rear axle
the biggest automatic transmission with a larger cooler.
jefe