I have recently purchased a toro Z500 54' deck 20hp cooler. I am having major problems with it missing grass. High grass or wet grass forget it. Jobs that took me three hours with a sixteen hp lawn tractor now take six hours to complete and I cannot charge due to the poor appearance of the lawn. Is it underpowered or am I missing other problems?? Have had to dealer four times with no satisfaction. Had the manufacturer involved and they say there is nothing wrong with the machine.