I had thought the same as Five Points...and guess what, I have the same model as you do (except mine is a 46") :ROFL
I have never had to adjust the linkage so I don't know but...Only twice have I had any problems with the hydro under load. And both times it really wasn't hydro related. The first was the "free wheel" pull rod at the rear. It was partially pushed in, and just enough to cause the valve fits and made it act like it was power related. I cleaned up the loose grass and dirt and no problem since.
Second time, thought it was an overheating issue so I cleaned up all around the blower fan over the transmission, and at the same time noticed that the drive belt seemed a bit loose and sloppy. Replaced that at the same time too. Not sure which fixed what, but the loss of power went away and my wife is happy 'cause it's her mower (she loves the hydro).