Zebra 3520 - trans or clutch issue

Anyone have any experience with a Zebra 3520 made by HMT? I was pulling out some brush and going from forward to reverse when it just stopped shifting. If I put it in low and first and crank the throttle up and then snap the clutch out it will roll very slowly but that's about it. If I leave it sit for a while, it will run fine again.

Any ideas? I'm also looking for a manual somewhere but can't find one. I appreciate your help.

Do all the gears work ?

Your description can be so many faults. Tell us what works and what doesnt.