I have a Hustler Excel 3200, the mower works great on level surfaces. I can be going full speed on level ground and start to climb a very very slight grade up hill and the mower will almost come to a stop. I have to pull back on the controls as the mower slows or the pump will whine. Also as mower slows I can feel the pulsating in the steering controls. Mower is full of clean fluid, new filter, new lines. Is there anybody who can help me fix my mower?