I did a 30-30-30 reset and things seem to be running better at the moment. Was still running CPU temps in the 80s but it sounds like maybe the heatsink on the R6700v3 just isn't that good and it does that. Putting a fan under it brought the temp down into the 50s.
I had formerly done a simple 7-second reset after installing DD-WRT because I read somewhere a warning against the 30-30-30 on some Netgears but I didn't find any such warning on the Peacock sticky so I gave it a shot. Putting "Resolved" in the title for now and will post back if problems recur.