I'm having similar problems. Also, when I am connected to a network or using Airodump-ng my adapter will disconnect or stop monitoring after a short time. Anywhere from 1 minute in to 40 minutes in.
Looks like it's dhclient causing my problems too. Is it possible to remove dhclient or stop it from running all of the time? I've tried killing it off - but it just keeps running, so I assume something else is using it.