in order to give you more accurate information having a full model and serial number off of the data plate would be helpful.

with that said....

there should be a function manifold on the same side as the hydraulic resivoir. First i would get some fitting caps and plugs and remove each motor hoses and plug them off one at a time, this test is to see if one of the wheel motors is defective. Since this is 4x4 all motors are tied together in the manifold circuit and cannot be accurately tested while all are connected due to the equalizing circuit that redirects fluid according to demand on each wheel versus the terrain.

if a wheel motor is bad once you unhook it and block the circuit off the other wheels should return to normal mode and all should pull evenly.

if you find all wheel motors are ok then you will need to go back to manifold block and check counterbalance valves and check valves related to drive circuit.