It should do somewhat better than that. Are you sure all the vacuum pods under the dash are functioning 100%. In particular, the recirc pod has three positions - 100%, 80% recirc, and 100% recirc. The small vacuum chamber that pulls it from 80% to 100% recirc tends to fail first, so you don't necessarily notice the difference. But drawing in 20% outside air will noticably degrade the ac performance. It's easy to check with a handheld vacuum pump/gauge.