Wheel Horse 724-Z transmission problems

I just purchased a used 724-Z. It runs great, but there is a problem with the right transmission. Sometimes when mowing, the right side stops pushing. I can pull the right handle backwards a couple of times and then the right trans straightens itself out. It seems odd that this pumping motion can cause it to correct itself. It happens quite often when trying to mow a couple of acres. I adjusted all chains, neutral springs, stops and of course checked the fluid. Everything is set as it should be. Can anybody tell me why the right side loses power? Thanks.

I think it may be one of two things. Low fluid level, like pumping the brakes or the hydro release on that side is not fully off. Could also be a loose connection, on the hydro pump. Sorry to say but I would take this one to a tech.