I know nothing about Ubuntu, however, I do have a 14z and have along history with the WiFi problems on it. Hence the reason I had a Google news alert setup which fed me your post. There's a number of posts in the Dell forums on the subject, which might come down to a bad design of the laptop. Dell has replaced my card twice and my antenna twice, then finally actually down graded the WiFi card to a 6300 (no bluetooth) to see if that would help. Kinda ticks me off that I don't have bluetooth now, but I'm still int he process of sorting it out with Dell and they have been nothing but great about everything. This card seems to be working better than the OEM card (6330, I think), but still not as good as my iPad sitting right next to it.
Some tricks (again, knowing nothing about Ubuntu) you might try:
- Turn off laptop battery power saving setting which puts card in low performance during low battery.
- Replace drivers with Intel's OEM card drivers.
- Enable Intel connection settings and mess with the options thereunder.
Best of luck. Oh, I guess I'd also suggest opening a support ticket to document the problem from the start.