1976 model 300. I’ve gone over most of the hydrostatic linkage, replaced roll pins and adjusted tension on the linkage plate. it’s all relatively snug. Very little play. The problem is I have a yard that goes up and down all over the place. No steep hills, but not flat either. When I’m going flat it’s no problem, but if I hit a slight incline or even a little rut The tractor slows down or stops. So I have to push the hydro lever foreword. Then it will maintain that speed till I start going flat or downhill then it will speed up to double the speed I was going uphill. So basically the whole time I’m mowing I’m constantly having to move the hydro lever large amounts to adjust my speed. Any ideas on what this could be? The only slop I can find in the linkage is a very slight amount where the pin for the linkage connects to the swash plate. But it’s not a large amount of play.