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See also (locked) thread:Only getting max download of 33 Mbps with new DOCSIS 3 Motorola SB6183 16channel modem and Premier upgrade
It took over a week to get to the right folks in support, but eventually the above forum post, mentioned to the @CoxHelp person I was Twitter DM'ing, made all the difference.
Hoping this forum post can help avoid some early adopter pains for other Cox customers who bought a SB6183. Let's hope they add the self-install menu option for this modem soon, so that proper provisioning would be painless.