I had the exact same problem with this router, couple things to do, first and foremost is the firmware but you say you have the newest, two are you using dlink wireless cards in your computers, if not you need to turn off 4x mode in the router and also make sure that under Advanced>Performace you need to make sure that Basic rates are set to no more then 11 Mbps. The 4x mode is under the same tab. Those settings are only gonna work if you use there proprietary cards which support up to 22 Mbps throughput. I use an Orinoco Gold Pcmcia card in my laptop and these things fixed my connection which was doing the exact same thing. (I work for a WISP so I deal with wireless daily) Hope this helps.