PW8 Upgrade

I recently moved from 500mbps to 1gig and, as a result, had to move to a new PW8 modem.  My old model and speed was fine...was just taking advantage of a promotion.  However, now that I've connected the PW8, which no longer has separate bands for 2.4 and 5G, some of my devices are having problems.  1 of 5 Roku Streaming Sticks I have is not connecting despite excellent signal strength.  My plug-in extender connects apparently, but when I move to that network it freezes...perhaps it can't handle either the new speed or the mixed signal?  Thoughts?  I thought was doing a good thing getting more speed for less, but I've hosed my old setup now and wish I could undo it.