Ultima zt1 hydrostatic trans issue, seems like over heating?

So I’m having my an issue with my cub cadet ultima zt1 54”. It has the hydrogear ZD-ANBB-7MDB-34PX trans. The mower is about 4 years old, and the last 3-4 times I’ve mowed, after about an hour and a half of cutting, the right side hydro starts cutting out. It’s fine with the mower is cool, but on a big yard it’s like it gets hot and wants to stop turning the right wheel.

I’ve put a new belt drive belt and re-adjusted the tension spring, but it’s still doing it.

I checked the oil level in it and the level looks correct, and does not smell burnt. It does not appear to be leaking anywhere.

The fan above it does have all of its blades, is it possible that it is not spinning and causing that side to over heat?

What is my next step towards diagnosing what to fix on this? Is it time to replace that side trans or is there a way to service this thing and fix what’s wrong with it without having to drop $700+ on a new trans for that side?