I want to say fuel filter but you did state that a long list of things have been done, I would think it made the list. If it didn’t, never rule out the obvious. It sounds like a fuel delivery issue and it appears that you have covered the right thing. There are electronic idle controls that must be checked using the appropriate scanning device. If you don’t have a scanner or a way to record fault codes there are some places like PEP Boy’s and Auto Zone who provide this type of service. The electronics should be checked.

Based on the mileage mentioned I would also check the timing chain for too much slack. If the valve timing is suffering due to excessive slack in the chain, that will effect vacuum which has an effect on the idle at low speed. I realize your frustrated over all you have done and seen no results. I am just trying to offer alternatives to help. I feel you have a fuel delivery problem at low speed. The basics need to apply, check all fuel lines and connections, make sure they are all tight.