My AC when it's 90 out will nearly run continuously. I'm just curious
if that is normal or if I have been undersized by the contractor
(installed a year ago).

I live in Colorado - dry climate.
We get a lot of direct sun.
The ranch has 1800 sq ft on the main level and a below grade bsmt of
the same size. Part of bsmt is finished, but we do not occupy it
often.

Mid June - end of August can have 90 degree days; seems like most days
are 85-95.

We set the thermo at 76 degrees. But if it's 90 outside and I try to
set below 76, it will never make it down until evening.

For mid 80s days, it's fine (remember we set our thermo at 76 though).

I'm concerned that a) the HVAC contractor has undersized my AC unit
and b) if a new owner preferred 72, it could not be held during our
summers.

I realize it's best not to oversize the unit, but with a dry climate
to begin with, removing humidity is not much of an issue.

Thanks,