2002 Ford Windstar dies on hot days

Recently had alternator replaced. Had fluids/filters checked-replaced in April.

Noticed this some last summer, but when Windstar is driven on a hot day, then parked, it will start but the engine will die. It won't idle more than 200-500 rpm and will die. When it finally starts to idle up to 1,000 while still parked will then die before I can get very far. Today, car died five times in the parking lot, and four times on the way home when traffic got slow.

This is the first hot day this year, and first time this year the problem has shown up.