I have one of those old Craftsman steel/tin yard carts that I loaded (not over full at all) with split wood to simply drive around my house to restock the front porch. I hooked it to the Cub Cadet in the lower driveway and went across the back of the house and turned up hill along the side of the house to head towards the front. The transmission started whining and the HST pedal starting bucking and jerking and motion ceased. I backed down, unhooked, attached the old Craftsman/Husqvarna with the Hydro Gear G730 and pulled the trailer around front with no issues.
That was the nail in the coffin. I will never buy a Cub Cadet again in my life. It had to go and I didn't overly care if I lost my butt to make it gone.
Cub may have once built really nice machines, and I may have had a factory dud... But I did change HST fluid and filter at 48 hours and this lack of transmission performance was seen both prior to and after performing that maintenance. I'm going to go ahead and assume that Cub is all MTD trash today.