Husqvarna HU700F FWD mower that I recently sold. He was not happy that the mower was not handling the steep incline. I checked and saw the wheels were spinning on the thick grass and seemed to have a mind of their own and wanted to wander but got no where (like ice.) I agreed to replace the wheels (that looked fine) and it was the same issue. I believe it is a weight issue. Is there an easy fix for this? Is this common with this model? The belt and wheels are fine and working properly, Thank you in advance.