My mom always got on my back for making T's into D's.

Your mom was the proverbial* King Canute stopping the tide. The tendency to voice unvoiced stops or plosives between vowels is a natural element of language change.

*But not the real King Canute. The real King Canute knew perfectly well that he was incapable of stopping the tide; he was trying to prove this very point to his sycophantic toadies.