Gees every one's tranny is dieing at the same time.
Park on the steepest ill you have
Get off the mower, set it to neutral and give it a push
A good tranny will be hard to push & stop the instant you stop pushing
A stuffed transmission will take off down the hill even before you push it
Get back with the results
The transmission section of the cub manual is near 100 pages
And when you get back please also post the model & serial numbers form the ID tag which for a 2005 model is probably on the left frame rail near the dash tower .