Help with shuttering G22

[purplewg]

48V, Plumquick motor, 500A Alltrax controller. Newer 4GA cables I put in 2 months ago.

The GF was spraying her pasture the other day and she said her cart stopped and would not go. Then she let it set for a few minutes and it started to go but has a really bad shutter both forward and reverse. She had been doing a lot of creeping. She had the sprayer connected to a separate 12v battery, not the cart batteries. Things I did last night.

1. Fully charged batteries and topped off their water.
2. Checked diode across solenoid.
3. Checked all connections.
4. I get the green LED on the Alltrax when I turn the key on.
5. Jacked up the cart and turned rear tires by hand. No noise or binding.
6. While still jacked up I ran the cart forward and it almost sounds like gear noise coming from the motor/tranny area as it shutters.
7. Checked each battery with a digital volt meter for any major drop when starting the cart. Max drop I saw was about.25 volts.

I forgot to look at the LED on the Alltrax controller when I had it jacked up to see if it complained under load.

Tonight I am going to drop the motor just to make there really is no gear problem where the motor messes with the tranny gear.

Anything else I can check or should look at? I would appreciate and suggestions. Thanks