That's exactly the difference between your trucking business and gas stations: If I'm not happy with your price, I have other options, some of which might offer a worse service for cheaper price. It's my choice to pay you more for your excellent service and reliability. You are not price gouging because I can shop around.
But there is really no alternative for gas. They all charge almost the same price in a given region, I have no other options. there is no competition. They all sell the same gas, No one offers a lesser product for a lower price that I can choose to purchase. The consumers see it as price gouging.