The 12hp I have will start up the hill and about half way it starts bogging then stops, you can feel it try but the wheels just stop turning and just pulsates somewhat. Belts not slipping or anything, just wont go and that's at full throttle !
Now the 17hp Im getting is a hydrostatic, so no more shifting gears, speed control at the pedal. It is a Scotts made by John Deere, so it should be a great mower as it was well maintained.
Im giving the craftman to my buddy, he is gonna swap parts as his rider wont stop, so all is a win win here.