I assume you mean 3.3 as 3.4 is not released yet.
Did you change the NmCaptureCallbackExitMode in NmConfigAdatper to ReturnRemainFrames? With this option, when your CPU gets behind, it will continue to process all the frames it's captured after you stop the capture engine. If you know the traffic you need has been captured, then the default option of DiscardRemainFrames is better for you.
You can read this blog for more info on our buffering.
http://blogs.technet.com/netmon/archive/2008/07/09/the-swimming-pool-and-the-drain-pipe.aspxThanks,
Paul