>> When i converted this show (it's ac3 audio in an mkv) with
ConvertXtoDVD 2.1 it worked fine... no problems at all.
Then i upgraded to 3.0.0.9 and all the audio is chipmunks on crack... the audio basically plays at double speed <<
Versions 3.0.0.1 - 3.0.0.9, copy the AC3 audio as-is. If that audio is based on a High-Def source converted to MKV, then it might be 640Kbps and that might play incorrectly on a standard DVD player. Because its not part of the standard DVD specs to support AC3 audio greater than 448Kbps.
If true, you might try converting the AC3 to 448Kbps and re-author the DVD using IFOEDIT.