What are options when there's oversized hvac?

I don't think my hvac installer ever did a manual j, they just switched out the same size furnace and central ac. I have roughly 800 square feet of conditioned space with an unfinished and uninsulated basement. Both the furnace and ac short cycle and I'm constantly battling with the thermostat. It's most uncomfortable during summer evenings when the temp is dropping but the humidity is still the same.

Obviously I can just find a new hvac company to do a manual j and have them install the appropriate sized furnace and ac but the units are only 4 years old and it will cost a lot of money.

Can I make some adjustments to the equipment so they run longer and at lower capacity? The furnace is a 2 stage. I don't know much about the ac except it is a 2 ton 15 seer.

For cooling, I hardly need anything because I'm completely shaded in. I live in climate zone 5 so there's a lot of humidity. Would it be wise to talk to someone about installing a whole house dehumidifier?

The house is a hundred years old but has had a lot of remodeling done and it is pretty well insulated (batts in the walls, lots of insulation in the attic, rim joists foamed).

Thanks!