Tech Blue - I would love to know what you are thinking. I will say though that when the 4 ton Goodwin 10 Seer 16 year old unit was working fine (up until the last month) it did cool down my house to the thermostat setting, shut off for a while, repeat. It was in fact meeting the demand. Even when I set the thermostat to 68*. If it was undersized I would guess (and that is ALL it is) that it would never reach my desired temp. My original thinking with the 5 ton was that it would not have to work as hard and therefore would be more efficient and last longer - but that was an incorrect assumption on my part.
What am I missing?