It definitely isn't it normal.
I don't have that problem on mine (my hours are just above yours) but I do lose a noticeable amount of power when the fluid gets hot.
My hydraulic pressure was a little low so I did raise it and that helped some. But there's still a problem somewhere. I haven't had a chance to really dig into it yet.
It would be nice to see if it only happens when there is heavy weight on the front axle, versus the fluid getting hot and thinner.