Toro Z5035 Left Wheel Doesn't Work Properly When Machine is Under Load

[Yelrah]

What I've done:
1. Added fluid to left hydro and purged. Before adding fluid the level was extremely low. I have not noticed any leaks and the fluid level has not dropped since I added fluid.
2. Lifted rear wheels off ground and checked forward and backward both with blades engaged and without. Works fine.
3. Checked tracking. Both sides seem OK.

Problem: With or without blades engaged left side does not keep up with right. With handle all the way forward or all the way back, left wheel does not turn. Can get left wheel to turn forward or backward (but very slowly) if I don't push/pull handle all the way to stop position. Was getting a squealing noise from left side but that seems to have gone away. I'm thinking the drive belt may be slipping under load but can't understand why it would only affect left side.

Any thoughts will be appreciated.

 

[BlazNT]

Purging Air from Hydraulics
1. Raise rear wheels off ground. Brace with jack stands.
2. Put bypass valves so it freewheels.
3. Get on mower start it and release the brake.
4. Push drive lever full forward for 10 seconds the full reverse for 10 sec. Do this 10 times for forward and 10 times for reverse alternating between each.
5. Return levers to the parked position and set brake. Turn off the mower. Move bypass valve bake to normal operation.
6. Get back on the mower and start it. Do step #4 again.
7. Return levers to the parked position and set brake. Turn off the mower.
8. Return mower to ground.
9. Test for proper working. If not repeat.
10. Check oil level and fill.

Let us know what happens. Lots of other things to try.

 

[BlazNT]

We need to the actual model number not the name of the mower.