A problem I've been fighting for a few years now and have not found a
solution.

Simplicity Regency 12hp lawn tractor (about 1996?- last year the
hydrostatic drive handle was in the middle). It has a mulching kit
(which is just a discharge shoot block) and I use 'leaf cutters' on the
leaves. When I first got the tractor, it did a superb job of mulching -
both the grass clippings and leaves in the fall. The lasts three years
or so, it has started leaving a trail of grass clippings down the
middle, and it take repeated passes to chop up the leaves in the fall.

I typically mow once a week.

I have tried all the following with no success:
Sharpened the blades
Changed the blades
Cleaned the deck
Leveled the deck
Tilted the deck forward and backward
Changed the drive belt
Cheched the RPM
Mow more often

Still it leaves unsightly clippings. The neighbor with a cheap MTD gets
a better cut.

Any suggestions? What have I yet to try?

Dave