Ok, so after doing some research, I found out some info. When I read it I actually remembered reading this before but I forgot...
The A535 is the older New Process Gear version of the New Venture Gear NV2500. Same transmission, different name when the company changed to New Venture Gear. These transmissions use 10W-30 motor oil or 10W-30 synthetic motor oil.
If you think it was changed by the PO, you need to be sure what it is, cause the AX-15 takes Mopar 75W-90 API grade GL-5 gear oil or equivalent. The NV3500 specifically takes Mopar Manua Transmission Lubricant P/N 4761526 or equivalent (I believe AMSOIL makes an equivalent).
Like I said before, you need to be sure, cause mixing up the fluids WILL cause failure.