lip sync motions delays as movie gets longer

[dennyj]

The lip sync works well but as the final export gets longer, the motion is delayed more and more. I can try to skew the keyframes manually but it's really tedious and it works perfectly at the beginning of the project. Please help. Also, I'm trying to export just a part of the movie (towards end where I'm trying to manually line up lip sync) but audio doesn't come through on a partial export (say from keyframes 1400-1600 for example. Thanks!