After a week the dealer phoned me and said it was fixed. He said all they had to do was adjust the pto cable. I said that could not have been the problem because the cable moved the lever all the way to the stop, but they insisted that it was fixed.
I brought it home, hooked up the cutter, tried it out, and nope, not fixed, pto still slipping.
I brought it back to them the same day with the cutter on and they tried it in tall grass and saw how it was slipping and said they will fix it but I haven't heard from them yet.