divx3 low motion with ac3 to DVDr audio sync problem

[at_mix]

I have 2 files in divx3 low motion with ac3 sound ( audio is in sync) . I join them in virtualdubmod with direct stream copy.
( audio still in sync ).

Demux the sound of the joined file w/ virtualdubmod. And use ac3fix to fix it.

Convert the joined divx3 file to DVD w/ mainconcept.

Use dvdmaestro for authoring and get audio sync.

what can i do to solve it? It must be the divx3

Thanks