Unable to have the full speed of my internet

I had trouble using my 5ghz signal using ac only (dd wrt firmwarev24sp2) despite being able to connect to it the previous day. Could no longer connect to it with the settings as described in previous post. I finally got best results using setting n/a mixed 80 MHz channel width, extension channel upper/ lower.

now consistently getting 120mbps down and 20 or more mbps up.