All good responses. Thanks for all the input everyone. In response to some of the potential issues...
I'm certain the problem is not leaky ducts. I've spent many hot afternoons in the attic tracing down each trunk, and duct to ensure there are no major leaks. In an attempt to fix the situation, one of the techs removed ~18 inches of dead space off the top of my plenum... Now the air in the house is much more balanced. But the problem isn't fixed.
The contractor has pulled a vacuum on the system and replaced with virgin refrigerant 2-3 times. So if there are incondensibles, they are hanging on tight.
The fan speed being set wrong is something that I'll suggest they check out. The house is kind of humid (~60%). However, I'm not sure if that is far above normal.
As for speaking with the owner of the HVAC company... I've dealt with him on many occasions. In fact he feels so comfortable with me that he has yelled at me over the phone on a couple of occasions.
**Update** After the last "fix" several days ago, my system has started making a very loud noise upon start-up that sounds like a furnace starting up or gas escaping (thats the best I can describe it). But we don't have any natural gas...
I'm going to call the contractor one last time today...maybe they will replace the whole thing. Over four visits in the last 3 weeks and the problem is worse (because of the noise) than when we started. And since the manufacturer informed me the contractor can be reimbursed for labor if the system needs to be replaced, I think replacement is a good option.