Hi Rob
I know it must be 'doing your head in' with having your connection speed of only 54Mbps instead of 300Mbps...
Here's the steps I took installing the 17.0.3.2 drivers...
1. I first disabled the old Intel -AC 7260 card wifi driver and Bluetooth drivers in device manager and made sure they were also disconnected in network connection section under change adapter settings.
2. I then uninstalled .the Intel PROSet/Wireless software followed by uninstalling the Intel PROSet/Wireless Bluetooth software ( I used Revo uninstaller for these steps).
3. I then ran Ccleaner to get rid of anything that was left over including left over registry entries followed by rebooting my laptop.
4. I then installed the latest Intel PROSet/Wireless software 17.0.3.2 followed by disabling U- APSD support in the advanced driver settings.
5. I then rebooted my laptop and checked on connection speed which was showing as 300Mbps, followed by doing a download speed test and a ping test to make sure all was well.
6. I then did another reboot followed by installing the latest Intel PROSet/Wireless Bluetooth software.
7. Finally another reboot followed by further checks and tests as mentioned above.
I would like to point you to an article I came across Wireless wi-fi 802.11n troubleshooting fixing tips
I hope this helps in some way or another.
Good luck