I'm not familiar with your particular unit, but I think I'm gathering that its a hydrostatic? I have a kubota L3301 hydro with a foot rocker pedal, bought it brand new this summer. In the summer (Texas, its very hot), everything worked perfectly. But we've had a few cold spells that dropped us into the 20's and 30's. First thing I noticed was that the pedal stuck in forward or reverse. Nothing is mechanically binding, and when it warmed back up it went back to functioning perfectly. So it must be a fluid viscosity issue inside the transmission. I'm not too worried about mine, its not cold near often enough to warrant throwing money at it. It seems I might have read something a while back about different viscosities for different climates.
Not sure what your climate is, I just figured I would throw that out there. If it matches your symptoms it might be something to consider if you don't find linkage problems
EDIT:
By sticking in forward or reverse, I should clarify that it doesn't just stick hard in full forward or reverse motion. What I mean is it is very sluggish to return to center, and doesn't always make it all the way to center. It may "stick" to where its barely creeping. All that is necessary on my setup is to slightly push the pedal in the opposite direction to center it up. And it clears up once the tranny is warmed up.
Which brings up another thought. You might check your manual if it seems to be temp related. If I remember correctly, my manual has different warm up times for different temperatures. I think for very cold conditions, its as much as 10 or 15 minutes before using it hard