There are programs like that. Deep Paint and BodyPaint (IIRC) but both are pretty expensive. You can also use UVMapper Pro together with photoshop and get sorta the same effect (I haven't tried it myself but it should work) Most people do like you do. It is tedious to make textures :o)

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.