Are you getting the same problem in all locations ? If you are seeing bad jitter and high latency across an entire network, as Andrea hinted at, this would seem to indicate that the APs are overlapping to such a degree that one or two bad connections are affecting the whole airspace. Drop your AP broadcast range and see if you can isolate it to a smaller area, more than likely its going to be stations that are affecting your network and not your equipment, if you can identify them, remove them from the network temporarily and bring your broadcast dB gain back up and see if the issue disappears.
