Yes there is, LovelyRandal! Precisely what that difference is in native speaker context, you'd certainly be much better advised to consult any number of educated native Polish speakers here.
All I might contribute to answering your query is that "naprawde" relates to authenticating the veracity of a given statement, "doprawdy" similarly, whereas "Ach, tak!" is more of "Ah, yes I see!", in that the speaker concedes to the statement by the interlocutor:-)
Hope this helps a little.
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