If the belt between the engine and the transmission is okay, then make sure the hydro-bypass valve hasnt slipped into bypass mode.
If you look under the mower, between the seat and the drive-wheels and are looking at the transmission, you should see a piece of 1/8" steel that protects the bottom of the transmission. On one side of that, you should see a piece of metal on the side of the transmission (maybe 1"x3"x1/8"thick). It should have a spring going from it to a stud welded to that plate, near to the bottom of the transmission. If there is no spring, or it has rotated away from the transmission, then it may have slipped into hydro-bypass.
Check the message we had in the Ferris forum, I am posting a pic from the manual of the bypass....
If you look under the mower, between the seat and the drive-wheels and are looking at the transmission, you should see a piece of 1/8" steel that protects the bottom of the transmission. On one side of that, you should see a piece of metal on the side of the transmission (maybe 1"x3"x1/8"thick). It should have a spring going from it to a stud welded to that plate, near to the bottom of the transmission. If there is no spring, or it has rotated away from the transmission, then it may have slipped into hydro-bypass.
Check the message we had in the Ferris forum, I am posting a pic from the manual of the bypass....