just a little on this;
I've got a house about the same size (~2200 , ~50 years old). System is about 5 years old and is a 10 sear, 2 ton. According to my very quick, very uneducated guess, the unit is on the small side for the size of the house. I have the original cheese cloth windows (read: energy inefficient) and two HUGE sliding glass doors, fortunately not facing either rising or setting sun. I do annually clean the outside unit with an 20% muratic acid solution to rid the coils of cotton wood funk and other crap. I keep filters changed and the inside coil is clean.
The system struggles this time of year and runs nearly constantly without stopping to cool the house to 74 degrees. The air balance is a joke. I have investigated and closed any leaky holes in the duct work, and had a new plenum built last summer (guy was at the house at built it cheap for cash-sheet metal, insulated sheet, mastic and insulated blanket wrapped for $150 complete).
I'm curious if the system is fine and the house (glass, insulation, doors, etc.) need attention or if I unfortunately have an over tasked system?