After setting for a week in humid climate the car starts and runs fine for 3 to 5 miles then it starts hesitating/sputtering (about the time it reaches operating temperature) for next 3 to 5 miles after that it runs fine. No problem again until it is not driven for a few days. Wiring has been checked, gasoline treated, fuel filter changed. Mechanics I have talked with do not have a clue. Car is garaged adjacent to Gulf of Mexico. While it is having the problem the engine runs reasonalby well while in park or nuetral but under load is when the problem occurs. Help please, I am very fustrated.

Distributor caps and rotors. Just a guess.

Probably the diustributor cap and/or rotor. Also carefully and completely clean the ignition coil tower-inside and out, along with all the plug/ignition wires and boots in and out. Salt air humidity is famous for causing 'wet start' shorts. You might try cleaning everything off real good by hand (including inside the distributor cap and coil tower), spraying the wires, cap, etc with a good silicone based waterproofing, coating the spark plug insulators with silicone ignition assembly grease before putting the wires on.
Sometimes the black plastic cover on th edistributor cap crascks and come sloose, making a perfect dust and salt trap for those wet mornings.

Salt spray residue that is invisible will collect moisture and cause shorts. Sometimes you have to replace the shorting component because the arcing causes 'carbon tracking' burns and it will continue to arc over at that track.