My computer is dropping Wifi Connection

MacBook Pro is dropping WiFi connection and not connecting 802.11ac.

MacBook Pro mid-2014 2.8 GHz

OSX 10.10.4

Airport Time Capsule Extreme

Firmware 7.7.3

Signal quality is "Excellent", but connecting only on 802.11b/g/n. Problem has appeared after updating OS to 10.10.4. WiFi log shows 5GHz channels open at 40 MHz but nothing showing for 80 MHz. Network Diagnostics says everything is working. Randomly loses WiFi connection completely although menu bar icon says connected. Not ISP because also lose connection to WiFi printer on the network.

Other devices connecting to the network correctly, so it seems to be the MacBook Pro only.

Thanks for any suggestions.