You can't go and randomly change the framerate of your source without a valid reason to... you have to make sure what the framerate of your source is first and foremost. Unfortunately the avtech has never been clear in how to understand what you have on your hands in terms of non-soft pulldown.
First thing is, in dgindex you should be doing "Honor Pulldown Flags" as the "Field Operation" under "Video", then you let it index, and then you check what the info is reporting. If it comes out with a very high FILM percentage (say, roughly 95% and up? Ideally even more, though), then you can go and reindex it with "Forced Film" as the selected operation. Otherwise you should keep what you have and then check if your footage is actually 60i or a 2:3 pulldown.
Since dexter is a live action source, it should be easy to find a good scene for checking this out; for anime this can mostly be done by checking pans and such highly animated scenes. The gist is that, if you have a 2:3 source, which is what you want to IVTC, you should be noticing a pattern of 3 progressive frames and 2 interlaced frames. This pattern of 5 frames should be constant in at least a whole scene (and like I said, it's quite easy to understand with live action footage). If all frames appear to be progressive or if all frames appear to be interlaced, then you don't have to IVTC; rather, in the first case you have a 29.97 progressive source, in the latter a 59.94 interlaced source. In the latter case you can choose to either discard a field of the two and edit at 29.97 progressive, or keep the bobbed deinterlace and edit 59.94 progressive (nowadays you always want to resort to QTGMC for your deinterlacing needs since how high quality it is).
In the case your source is a 2:3 pulldown, however, you WILL want to IVTC (and thus bring to 23.976). You can do this by doing even a simple chain such as tfm().tdecimate() really (the results won't be absolutely perfect, but still good enough; especially with live action it should be easy enough for tfm and tdecimate not to get the patterns wrong since there's not the issue of having footage animated at an "actual" framerate lower than the "nominal" framerate), and the audio will keep in sync with what you have.
If you still are uncertain of what you have at hand, posting a sample m2v (you can make a small one by using the [ and ] buttons in DGIndex and then selecting "File" > "Save Project and Demux Video") will
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