I've been speaking with a number of other friends/family/colleagues that also picked up Surface P3s on Day 1 and they seem to be having the same issues. 802.11ac compatibility seems to be the worst, but even 802.11n speeds seem to be worse than other stable devices.
Try downgrading the driver.
of course, this is just a workaround.
It is disturbing that there have been no replies from Microsoft here in this forum that 1. acknowledge the issue and 2. state that engineering has repro'd and is working on a fix.
Agree. In the positive side, nobody has came saying that you don't know how to use the device.