Hi Blue70SS,
The 336 is simply the constant of conversion from mph to rpm and inches (and/or vice-versa); it is not related to rear axle ratio.
so for example (using say 6th gear):
TR6060 6th = 0.63
your rear axle = 3.25
using engine RPM:
gear_ratio = 3.25 * 0.63 = 2.0475
road_speed[mph] = (engine_speed[rpm] * tire_diameter[inch]) / (2.0475 * 336)
using have transmission output rpm:
road_speed[mph] = (trans_output_speed[rpm] * tire_diameter[inch]) / (3.25 * 336)
I don't know if there's a pid for the M6 trans output speed in RPM.