Husq. 22v46 losing forward drive power

I have a Husq 22v46 riding mower. Recently, I began losing forward drive power on any kind of incline. Typically, on flat ground, it powers fine. When going up a slight incline (it used to power through these inclines), it now loses drive power (not motor power).

Any ideas on what I might check to remove the problem? Can't tell if it has drive oil that I need to check.

Husq. 22v46 losing forward drive power