Where is this located and what are the ambient temperatures?

I missed that important detail, didn't I? East Texas. 99-104 degrees most of summer.

Brick house, horizontal system in attic, hard-pipe, no shade trees. Faces south with most windows on the east side or under covered patio on the north side.

Does the condenser sit in the sun all day? If it is 104 degrees in the shade, then it must be 130+ in the direct sun. The unit may not be able to operate under these severe conditions.

Try giving the condenser some shade and see if it performs well at 5pm.

unreal that you have to come to
online hvac forum to solve the problem.

there isn't enough info for anyone
to do more than your company has..
take a guess.

has your company any experience with foam sealed
attics? is the gas furnace self condensing or
does it have 80% furnace with combustion air
added to unit?

to me...the starting point for a/c performance
would be to see if air provided is being delivered
into the living space of the house. not leaking
into attic.
then using data loggers, set up to take hourly readings
to track how often unit is comming on
and how much humidity it removes during the
run cycle..and how much RH increases between cycles.

send tech...in the afternoon...probably next summer
unless we get some hot December afternoons.
sending tech before 2 pm to troubleshoot these
problems is just pissing away homeowners time & money.

in high summer the unit should run continuously
from mid afternoon into evening. with that 500 sq
ft per tons sizing the unit probably runs 5-15 minutes
and doesn't remove enough RH for comfort.

if equipment is correctly installed, then you
work from there to eliminate problems.

if you can't solve the problem..recommend some
one who can. call someone who can test house
& ducts and do a house diagnostic service.
keep their contact info for future use.

comfort institute, RESNET, BPI have trained
people who solve these issues if it is
beyond the abilities of your company.

best of luck