I've seen these before, GF is a front cut. If the PTO is Hyd driven, and it cuts out while you lift the deck, it sounds like there is not enough hyd oil supply to run both the deck and the lift. I assume this is a new problem, and has not always happened since you got the unit. I would start with hyd filter(s), just to be sure there is an ample supply of oil. I have seen a similar problem on a front cut because the filer was damaged- it was dented in pretty bad and didnt have the right amount of oil being supplied.