Timeling drags after publishing with sound from files

Hello all,

This is the first time I have worked with narration. I added the audio as files that were recorded in Audacity and converted to MP3 files. I worked hard to sync up the sound with the animations, and It seemed to behave nicely in the previews. Once I published however, the audio "sped up" and was no longer in sync with the timeline trace. Slides end 5 - 10 seconds after the narration quits even   though the timeline shows the slide objects ending with the narration.  What gives?

Some additional info: The Original Publishing preferences were set to "Custom" by default and the audio rate was 128 kbps. After reviewing the original published version I set the preferences to "Standard" (48 Kbps) and there was no change in the narration time.