There was a thread a bit ago about mulching blades, I figured I'd repost what I said there, may help somebody:
There's a deep rabbit hole to go down into, in regards to what type of deck pairs best with what type of blade. Some are just more compatible than others. This year, I started running Gator G5 blades on my Bradley stander mower, awesome results. It's a heavier/wider blade with a slightly higher lift compared to the Stens mulching blades I had on the Bradley, but then the machine is commercial grade and has the torque and spindles to handle a heavier blade, and seems to even prefer the higher lift blade. Some deck designs can handle the weight of a heavier blade, but just don't like a higher lift blade, meaning your cut quality will suffer (either due to the blade, or the deck gets rapidly caked with grass clippings).
Also, there's the deck design. The o/p mentioned his accepts a mulching kit, so I assume his deck has each spindle bay partially baffled, with the discharge channel running down the center and out discharge chute. The partial baffles allow for the grass clippings to remain in each bay long enough to get pulverized by the serrated fins on a mulching blade, that's the idea with that. But those fins are what produces the airflow, sucking up the grass, and discharging it. Some decks don't do well with a higher lift blade, because the increased airflow on them spits out the clippings before the serrated part of the wing on a mulching blade could do it's thing.
Or vice versa, it's so effective with mulching that the deck soon gets caked with clippings, and your machine starts bogging down and/or leaving trails of windrows. That's why I'm asking if you got the chute open or closed. Whichever way it is, try it the other way.
