Howdy! So I have a z254f I bought about 3 and a half years ago, and have been having issues with how it cuts since we converted over to mulching blades. We bought the OEM mulching blades, put the baffle off, and ever since no matter what I do, it misses a stripe. Doesn't matter how high or short the grass is, etc. I've had our repair shop look at it, level the deck, replace the blades, and zero luck. I'm wondering if maybe it's an issue with the blades themselves? Has anyone else had any similar issues, and if so what blades did you swap to that helped?

I mow every 3-7 days, on a 4 or 5 for the height. Grass is fairly thick, and grass type if I had to guess is fescue, mixed in with some standard weeds etc. (It's a yard, not a "lawn").

Any help is appreciated, as I'm tired of having to mow 2-3x to make it look half decent, as that gets time consuming with an acre and a half.

I have Gator mulching blades on my 42 Toro (2 blades) zero turn.
 
There's no problems with the cut however with the "chute cover" on the grass 
would want to not discharge fully.  So now I use those blades  but with the side discharge 
chute installed.
 
As for your machine, I'd get it on the garage floor and raise the deck.  
Get all three blades as close to tip to tip and measure.  
 
They should be within (IME) 1/4".  If the middle one, (which sounds like the issue)
is off, or perhaps the deck / spindle bent that'd be something to look for..
 
Did you get an even cut with regular blades?
 
.

Honestly I don't remember having this pending with the regular blades, but it's been quite a while since I had them on. I had my small engine guy check the deck and it is level and he sharpened the blades etc and did an inspection and didn't find anything, but I'll have him take a look specifically at the tip distance and spindle etc.

I'm not sure how he measured the deck, I hope it's at the blade tips (tip to tip).
 
You can easily check that yourself..
 
I had a 60" commercial machine come in with one side cutting way off with when he he went back for another cut.    Besides adjusting the side adjustments, I had to raise the deck on one side by one "adjustable hole" (towards the rear of the deck, left side).. I set the deck as noted below..
 
Also, there's several ways to set up the deck. 
IE, the tips of the blade are LOWER pointing towards the front of the machine is popular.
 
I have mine set dead level with the ground (front to back).  The cut is very even,
seems to cut well W/O the machine complaining...   
 
If not set up that way, you may want to try it