He DID do all new small parts.
I think the issue comes down to Motive specifying a target 0.008" and minimum 0.006" backlash clearance.
Notice that Kodiak apaprently specified 0.003" clearance. That would make a big difference in noise level.
When I talked after the install to the Motive factory tech service rep on the phone, complaining about the audible noise, he said that while there IS going to be more noise with 4.56 than with 3.73, it should not be objectionable in volume. He said not to go tighter than 0.006" on clearance, in order to ensure that the gears are not so tight that they bind when get they hot (e.g. sustained high speed or sustained load), as they get larger when they get hot. In other words, more clearance is safer while being noisier. He said that what sometimes occurs is that the clearance gets a bit larger as the gears break in, and advoised that we should re-check it now, and if necessary, reshim to get back to target, or minimum (but no tighter).
He DID say that if the gears were not properly clearanced by the installer, or were not properly broken in, they COULD have been damaged, and thus be making noise (like a worn rear end would do). But the sop that did the work is one of the 2 best in the Atlanta metro, builds highend engines, and has done rear axle changes a LOT for over 20 years, and the work was personally done by one of the owners (Lamar's son Rob) so I doubt there is an expetise problem. Rob also told me he broke the gears in on the dyno at moderate loading for 40 minutes.
The Motive tech guy's theory about the clearance increasing makes some sense, as my noise gets completely inaudible when the vehicle has run maybe 10 miles at high speed or into a good headwind, but never gets quiet arpound the city at low speeds, even after prolonged use. My theory is that when the gears get HOT, they get to the ideal clearance, so a bit less clearance than what we ACTUALLY have now is probably the right clearance.
At any rate, the feel and performance of the SSR are SO improved with the gear swap that there is no way I would consider undoing this mod, noise or no noise.
Note that the noise I am getting is mostly masked if the AC fan is set to 3 or higher, and completely masked by any sound system volume at all.
Jim G