I bet you when the tech said it was overcharged by 1 1b, it wasnt an exact figure, that 1 lb if it was, was just to get his readings correct. If the system was off for alittle while, the ducts would be hot giving a higher temp loose from the A/H to the air outlets. There is going to be some increase in temp when the ducts are in a hot location, from the time the air leaves the A/H to the time it exits the air outlets (7 deg is alot). The tech that came out was mostlikly from the installing contractor and is not going to say anything too negitive if the system was undersized. IMO, unless you have a very well insulated home and is some kinda energy eff home, and is sitting under a blanket, I usually (depends) use 400-450 sq ft per ton, sometimes 350 (they used about 700 Sq ft per ton) I am not a big resi guy, and would not be able to to a load calculation for you on the computer. I see your not going to get too much sleep over this. Bring in another HVAC company to help you out. The system may be able, w/ some very fine tweeking, to do alttle better, I dont think so though, it sounds some what small.