Rank 5 is when the real grind begins, so don't get discouraged that you are feeling stuck, progress gets way slower against better competition and with no win streaks.
Your deck is generally fine. Standard pirate lists usually make something like the following changes: -1 mortal strike, -2 naga corsair, +Finley, +2 southsea captain. At the very least get Finley in there.
The trendy 'water' build with murlocs looks something like: -2 mortal strike, -Leeroy, -2 naga corsair, -1 deckhand, +Finley, +2 Bluegills, +2 Warleaders, +Finja