Welcome to rider ownership. Three blade decks seem to present more quality of cut issues.It should go without saying blades sharp, deck clean, throttle wide open and mowing at a speed that allows the deck to do it's job. Hopefully the proper blades were installed on your deck. You can also experiment with different style blades. IE bagger, mulch, gators etc. In fact, I had a client with a 46" deck, that gators cleared right up his straggler issue. Next, you get to play scientist and change the pitch of your deck. Why your at it, go through the manual and try the level side to side and pitch by their instructions. The final pitch that correctly mows YOUR lawn may not be what is shown in the book. Standard pitch is always assumed to be "slightly lower in the front". That can end up being pitched even rearward in the end. It is always a trade off moving the deck one way or another. Sometimes striping will go away and stragglers will present themselves. Scared yet? If you bought this from a servicing dealer, talk to them and see what they are willing to do.
Q