Sorry to the OP, what a pain in the butt.
Your choice of a rinky dink dealership who doesn't even have a service department is the root of your trouble here. They obviously botched the 3rd function install and are deadheading your tractor hydraulics somewhere, which is robbing your power.
Sure, you might not be able to run high-range up a steep hill, but if you can drive on flat ground and move your loader around, the entire tractor hydraulic system is suffering badly. Why did you think it was ok to keep using the tractor in this condition? STOP USING IT UNTIL FIXED!
Folks, when buying new : VET YOUR DEALER. Demand to see the service shop and meet the staff. Ask questions.
But back to the OP - try not to get your clams all steamed by things taking a week at a time. This is normal. The mechanical issue here must be rectified, but be aware - it is going to take more weeks of downtime. Hang in there.