Is your attic air sealed and insulated as needed?

Yes it is insulated, 1994 standards, not sealed however I am not familiar with that term

Also, did your AC installer or sales person do a load calc for you?

They were really professional as were the two other bids we got, they were all pretty similar, I am thinking maybe we just assumed the coverage would equal over both floors.

I had the same issue with my 1950s built home that I just moved into. Whenever I was working in my second floor office or trying to sleep I’d have to run the cr*p out of my HVAC.

Estees came through and suggested adding R13 to my attic since it only had about an inch and a half. They added 12-13 inches to the existing and it was an instant change. Before the addition, I’d have to run my AC at 70 and it would run to death all night and would be freezing on the first floor. Now I leave it at 74 and we’re all very comfortable.

Do you have an air return on the second floor? Did your AC installers check the second floor supply vents? I'm another Seattle-area homeowner who can tell you from sad experience that the ducting that's adequate for heating our homes is not adequate for cooling. We have no upstairs air return, so the heat rises and just stays there. We're getting a second-floor air return and an additional supply duct installed as part of a larger remodel.

Aside from ductwork changes, your options are additional window units or minisplits for the second floor. We do a mix of two window units and some people camping downstairs when the weather is hot. Check out the GE Profile/Solera type window units. We put one in our MB, and it kept the room very comfortable through last week's 91-degree weather. Much quieter than our portable unit.

Beside good insulation, I found that the key is good air circulation and closing of blinds in rooms that gets the hot afternoon sun. Heat rises, cold air falls. The thermostat only measures the air temp in the spot it is at, not the whole house. The ceiling fans are on where we have them and the rooms that don't have ceiling fans we have just have regular fans. The vents in the basement are shut off. Even at our camp which is one story we use the same principle. It works good for us.

Where is your master suite? Might it be over the garage? Isolated rooms like that can be harder to cool.

I’m in a 3600 sq ft, 2 story, with 3 large and adequate A/C units. And, yes, I still keep all the blinds/shutters/curtains closed. I feel it helps to keep inside temps down at least a few degrees.

Have the HVAC people check if all of the dampers are working. If they are stuck in the closed position, then that would be the problem.

We do have a cold air return upstairs and I believe sufficient insulation although the MB has high ceilings. Would it mess things up to close all vents to rooms that we are not using to boost circulation elsewhere in the home? Maybe our expectations were a little bit too optimistic. Thanks everybody for the suggestions, I appreciate it

You should check with the AC installers before you do that. Closing vents can cause pressure issues and damage the AC unit. You might want to tag this thread to the HVAC board, not just Design Dilemma. The pros on the HVAC board are very helpful.