If your metal box really didn't have any insulation, there should be condensation on the metal from the cold air in direct contact with the metal.
You have to have someone do a capacity check on the system; this will tell you if you are getting the correct amount of BTU cooling at the evaporator. You might have a large latent heat load (humidity) which takes away the sensible (air temp) cooling of the unit.
A leak in the return side would pull in hot attic air and increase the load on the a/c unit. If you can hear any whistling noises around the unit, there is a leak.
Also, the supply register temperature should not be much higher than the air coming off the coil. I THINK 2 deg is max.(I'm sure I'll be corrected if not).