What did you convert from? If it is an avi file with MP3 audio that uses variable bitrate encoding, that is probably the source of the problems.
You can extract the audio with VirtualDub if it is avi…save the audio as a .wav file and use this extracted audio as your audio input in TMPGenc when you encode to dvd again.
If you want to try to fix the existing dvd, you might try the free trial of VideoReDo TV Suite. Use the Quickstream Fix tool within that program to get the audio and video back in sync.