All of the other advice is good, but I think the answer is pretty obvious to me.

If you're running cold on the freeway (as in, its working properly), but not at idle, its either a problem with airflow across the condenser, or the compressor isn't working well at lower RPMs. Checking the high side pressure will sort out the second scenario.

Now, you say you had the aux fan replaced, but if the condenser is clogged with dirt/debris, it won't matter much. Take a look at how much dirt you see in there, and maybe try to hose it out from the back.

Here's a quick test you can do before you buy any new equipment - at idle, turn on the AC and spray a garden hose on the condenser. If the AC turns icy, you have an airflow problem. If it stays the same, you have a pressure problem. Good luck with it!