Here's a quote about the price being slower going down for gasoline:
Prices also tend to fall more slowly than they rise, a dynamic known as asymmetric price movement. When costs increase, retailers adjust quickly to reflect higher replacement costs for the next delivery to their station. When costs decline, prices adjust more gradually as stations work through inventory purchased at earlier, higher prices, but competition among stations gradually pushes prices down over time.
Competition between gas stations "gradually" pushes prices downward. Sounds like there may be a unspoken rule to keep the prices from falling rapidly as they are all benefitting from charging higher prices while paying lower prices for gasoline, keeping the profit, while the customer is paying higher prices artificially. Nothing new as this has always been the way.