I experienced the same problem, on AC routers the connection is not stable and slow. For a device that is supposed to be cutting edge and costs over $1,000, Microsoft is putting the nail in the coffin by releasing it without properly testing the wireless
adapter (once again). My main issue is that this is the same problem that Surface Pro 2 had and it is carrying over the new device as well. It does not make sense that my $200 Nexus 7 has a better WiFi adapter and software than the $1,400 Surface Pro 3.
Even inexpensive touch based notebooks with Windows 8.1 ($450) are much more reliable than the Surface Pro 3.
Microsoft Support says there are no issues with AC routers and that it must be my router and/or a defective tablet which was already traded for a new one and still has the same issue. They recommended that the only solution was to either restore from Factory
and disable windows updates, or return the device for a refund.
Disabling Windows updates is not a solution to the WiFi (Limited Connectivity) and poor performance problem.
I have been trying to support Microsoft because the Surface Pro line had some cutting edge design features, but a product is only as good as the company behind it.
Rolling back the WiFi driver does not work, and why would I want to spend hours re-installing all the software again just to disable Windows Updates and "See if it works". This is why users will start to switch over to another OS, I don't want to, but I
don't have the time to be beta testing Microsoft devices / OSs.
Hopefully Microsoft is listening and fixes the problem. It may be too late for people that had to switch.