Inspiron 15 7000 WiFi issues

I have had my 7537 for 2 days. All seems OK but struggling a little with Wifi.

Whenever I try to connect to an AP it says taking longer than usual and then limited access.
I have tried this on 3 different wireless AP's and it does the same on all of them.
The connection does work at full speed but only if I am in the same room as the AP if I move to the next room, signal strength still shows good, but speed drops from 12Mbps to under 1Mbps.

I have installed Windows 8.1, upgraded the bios to 05 and installed the new 8.1 drivers from Dell but I still have the problem.

I have also tried uninstalling the N-7260 and all the driver software all the way back to the original Microsoft one and then re-installing the latest Dell/Intel® PROSet/Wireless driver but it did not make a difference.

I tried the windows 8 driver in computability mode fix but could not get that to install.

 Anything else I can try?