The power is meant for cutting the grass, not pushing or pulling heavy loads.
My LT180 has the K46, yes it needs a tranny oil change/possibly new parts. It is a 2005 model, so it has worked for 14 years so far.
You might try heavier weight oil in the summer.
I'm not sure I can go heavier than the 5W-50 recommended by Tuff Torq. Are you aware of a heavier oil that would work in this unit?