New Install Nightmare - Need Advice

My house is around 5400 sq ft (3600 basement/downstairs and 1800 upstairs), located in Northern Va, and built in 2002.

Downstairs/Basement Unit:

4 ton Lennox XC-20-048-230A-01

SL280UH090V60C-04

CX35-49C-6F-1

Upstairs Unit:

2 ton Lennox XC16S024-230-04

SL280UH070V36A-05

CX35-36A-6F

Anyway, the downstairs unit can keep the house at 71F with no problem, but I've been miserable upstairs. Every day for the last two weeks has been in the 95+ range, and my system up in my master bedroom is only getting to 77-78F with the t-stat set for 71F. It seems the rest of the upstairs is cooler, but my bedroom is located above garage and below attic.

The installer has been out several times and says the system is operating fine (proper refrigerant/air flow/no duct leakage/etc) and says the reason for the high temps is due to infiltration from my 2 - 4" exhaust fans located in the master bath because they don't have dampers on them, and from infiltration from three windows in my master bedroom. They're recommendation is to install dampers on the fans and replace my windows. I'm thinking WTF? I even had a window company come out and said the windows could be replaced, but there's no way the 7-8F temperature differential in my bedroom relative to the rest of the house is from the window infiltration (he's not an HVAC guy though).

My question is do you think they undersized the upstairs unit? The 4 ton downstairs is fine, but the 2 ton upstairs is not keeping my bedroom cool. The guy didn't do a Manual J and used around 1000 btu/sq ft for my newer house to size the units. It's apparent this heuristic is not applicable to my house due to the terrible windows, not to mention that my master is above the 3 car garage and below the attic, so it's not receiving air conditioned air like the rest of the upstairs. My attic has R30 insulation in the attic, but I'm not sure what's below the floor joist above the garage.

What do I do? Is it even acceptable for them to recommend me replace all these items when they were the ones sizing the unit and should have realized the condition of the house before making a sizing recommendation? Thanks in advance.

submitted by /u/uMAADBr0
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