The sudden draw of power from pushing the HST pedal to the floor can overwhelm the engine if you don't have the RPM up already. Some HST equipped vehicles have a "linked" pedal where the HST pedal and engine are linked so engine rpm will rise with the HST pedal pressure. I skipped the linked pedal option, so I have to manually move the fuel/throttle lever if I want to go faster than the engine can keep up with. It's kind of like trying to take off from a stop in third gear in a manual transmission car if you push the HST pedal to the floor without having the engine RPM high enough.That's what I use to do with the Rhino, with the HST it's a whole different ball game. With the HST if you do that you'll lose power so with the Kubota you just walk up it nice and slow in low 4WD.