2010 Craftsman 54" YT4500 Loss of drive

[Rockin' G Ranch]

The mower will not go uphill and at times barely moves on flat ground. Seems to have more power in reverse than forward (but not by much). There is no noise or any indication that the belt is slipping.
Think it's the Hydrostatic Transmission gone out?
Couldn't find where to check for fluid to see if it was low.
Any ideas what I should check?
Thanks.

 

[Fish]

first, wiggle the bypass switch, and see if anything changes...

 

[Rockin' G Ranch]

first, wiggle the bypass switch, and see if anything changes...

I did - no change. Thanks for the response.

 

[Rockin' G Ranch]

UPDATE:
Technician came out and found dirt/trash under the frame keeping the clutch/brake from completely releasing. You cannot see this area unless you turn the tractor over. It is located right under the clutch pedal.
He blew out the trash with a piece of small ID tubing on a air compressor line (he encountered this problem so many times before that he built this attachment for it).
Nothing at all wrong with the transmission.
Now I know where to look if it happens again.