Kohler K91 Owner's Manual page 224

TRACTOR OPERATES IN BOTH DIRECTIONS, BUT WITH LOSS OF POWER.
CONDITION BECOMES WORSE AS TRANSMISSION BECOMES HOT.
INSPECT O I L
SUPPLY
C O N T A M I N A T E D
CLEAN SYSTEM
AND REPLACE O I L
I
J
I
LOW
DEFECTIVE
RELIEF VALVE DEFECTIVE
O K
INSPECT IMPLEMENT
RELIEF V A L V E
DEFECTIVE
INSPECT COVER MISSING
INSTALL THRUST PLATE
AND REPLACE CYLINDER
BLOCK ASSEMBLY
THRUST PLATE
O K
O K
O K
INSPECT PISTON W O R N REPLACE CYLINDER
BLOCK ASSEMBLY
O K
INSPECT CYLINDER
BLOCK ASSEMBLY
DEFECTIVE
O K
I
I
O K