John Deere 317 binding when pto engaged

I have a John Deere 317 with a Kohler KT17QS. After the mower deck has been engaged for a few minutes, the deck seems to be binding somewhere and slows way down almost to the point of stall, especially if going up a slight grade or in thick grass. As soon as I shut the pto switch off, the engine goes back to full speed. I checked all the bearings in the deck (all good) and the mule?(also good) so its not bearings that are binding up. Could this be the electric pto clutch that is bad? If so, is this difficult to replace? or time consuming?