Hello again, I still need the full model number of the outside unit, that will tell me its cooling capacity.
Here is a list of things that will cause poor humidity control,
1. a slight over charge of refrigerant (even just 2 or 3 ounces)
2. Cooling system is too large for the home, and so comes on and cools
the house, and goes off before it has time to reduce the humidity.
In your case a system that cycles more than twice an hour on a day
over 98F outside would be slightly oversized, and if it cycles 4 or 5
times an hour it would be grossly oversized.
Those are the two most common errors... the fact that the installer has recommended replacing the thermostatic expansion valve is a red flag, along with other factors... nothing related to the expansion valve will cause these humidity control issues.
We can go from here if you wish