Thanks, its weird because i have already cut for two months with no issues. NOw when I took it apart and cleaned it, suddenly i lose tension. Its a V belt, so maybe I will flip it and see or even tighten the from screw bolt that holds the front of the deck by a kotter pin. That should add some tension. Blades are tight and everything looks fine. else will just go and get a new, slightly tighter belt.
As for your deck height comment, so the idle/tension arm, as you raise the deck height, the distance the belt has to cover shrinks a little?