Getting only 54mbps on a 5Ghz AC network

Solution? There are two.

1. Switch the WIFI security settings on your access point to use only CCMP (or AES).
2. If 1 can’t be done, on Windows 10, you can force the use of CCMP (AES) via the wireless properties.

Why?

Apparently the TKIP cipher is not compatible with higher data rates offered by the n and ac standards, as explained in this StackOverflow answer. Also, if your router broadcasts that it supports both CCMP and TKIP ciphers, for some reason Windows 10 will prefer to use TKIP by default. Why? I don’t know, but Windows 7 seems to choose CCMP by default.