My Z-trak (f620) seems to want to pull to the right when both sticks are depressed fully. Is there an adjustment for this, or is one of my drive motors weak? Both sides work strong by themselves, but in order to travel straight, I have to constantly readjust my push. Also, does anyone recomend a drive tire with better traction for side hill and/or slopes? I wanted to get Bar tires, but realized that they would tear turf in ZTM mode! Thanks guys.