Having a problem with Audio Sync.

The source is a DVD

I use DVD2AVI (Forced Film, YUV, Demux AC3) and then TMPGEnc to reencode the video.

When I author (using DVDlab) I load in the AC3 track from DVD2AVI and the video from TMPGEnc.

The audio is out of sync both on the resultant DVD and if I play it through PowerDVD before I burn. By as much as a second.

How would I go about fixing this ?