My guess is that it might be a god idea into changing out your RD cables. Sounds like there's something is really making things stick.
However, before you go and do that, undo the cable and see if you can move the derailleur manually. If it seems to move/shift ok while manually moving the derailleur, then more than likely, the problem is isolated to the cables.
However, before you go and do that, undo the cable and see if you can move the derailleur manually. If it seems to move/shift ok while manually moving the derailleur, then more than likely, the problem is isolated to the cables.