Yes, it was charged with R12.

I am starting to think it needs more refrigerant.
Also, I am going to take a look at the condenser cooling fan. The fact that it is better at highway speeds is leading me to believe that maybe that fan is not coming on and the highway air is cooling the condenser.

At the end of my 125 mile drive today, I left the a/c on and opened the hood and the fan wasn't on.