Once upon a time there were forward & reverse adjusters on ZTR's
The techs were supposed to run full forward for 30' then full reverse for another 30 '.
If you end up more than 1 ' left or right of where you started the bars got adjusted.
That got dropped pretty quickly because it was near impossible to do and would change as the units got hotter.
It was also only good on hard dry surfaces, which do not seem to grow much grass.
Now do that test.
If you end up more than 10' sideways then you might be getting a problem with your trannies
Otherwise use the thing between your left & right ear to compensate .
There are adjustments on the tranny to vary the amount the lap bars move the levers.
You make adjustments 1/12 turn at a time and on each side so 1/12 tighter one side & 1/12 looser on the other.