Joining Mpegs

Have a question for you… I have a Svcd 480X480 mpegs parts and i am using Tmpgenc plus 2.5 to join them… But my problem is after i joined them together it plays choppy and the audio doesn’t sync at all… I thought it could be my parts so i loaded up powerdvd and played the files (part1 and part2) and they play just fine without any sync or choppy problems… Could anyone elighten me on what could i be doing wrong…