You are correct in that the pressure is probably too high. Most shops and a dealer in my area only fill to suggested capacity LESS .3 lb. as the Nippondenso compressors are fragile to say the least, and too much will kill one and too little only cools a little less! Your choice, be cool or pull out your wallet!
Try the WaterWetter product in your radiator also to cool it better as the AC condensor
(in front of the radiator) will feel the
radiance given off.