Hi guys, this is my first post!

I have acquired a 02-FG30 that was on its was to the scrapper, it starts and the hydraulics work, however, there is no drive! Things I have checked...

Trans fluid, level but old
Forward reverse arm on the gear box is free moving as is the inching pedal.
The truck rolls so I'm certain the brakes are not binding to the point of stopping it from moving.

with both wheels off the floor they do nudge forwards/backwards but do not continuously spin, nor are there any bad noises actually from the transition.

My experience with torque converters and more traditional style gearboxes is limited as I mostly work on Lindes with Hydrostatic drive. Is there anything else I should try or check? I am capable of removing the engine/gearbox if this is required!

thanks in advance :)