Zero Turn Mowers

When going up a hill the back right wheel doesn't have any power and starts making whining sound. I can let the mower set over night and it works Ok for about 30 minutes, but starts doing the same thing. The dealer said to disengage the wheel EZT by-pass linkage while the mower is running and push the steering levers forward for about 15 seconds and then pull them back. That would get the trapped air out of the hydraulic system...I have a Zero turn RZ5424

Didn't work???? Any other suggestions?

Thanks
Robert