Ok I was introduced to Switch (an audio conversion program) and it takes care of my audio problem. Now for yet another problem

. My video is being sped up, from 21 1/2 minutes long to 17 1/2 minutes long. Here is what I'm doing:
Using MKVextract to pull apart the file
I take the two audio tracks and run them through Switch, turning them from 5.1 AAC to MP3 192 stereo.
I use MKVmerge and mege the two new MP3 tracks with the old Divx video that came from the original MKV and also the srt file
What I get is a new MKV file with basially only the audio tracks switched out
Now when i read these files with mediainfo, it says both the original and my new one uses 29.97fps Divs video. But when I play my new MKV the video is moving fast. It starts out fine, then 2 seconds later its already four seconds ahead, and it just continues to speed along. The music and the subs however a\is still ok. Any idea how to slow the video down?