The Department of Energy (DOE) reported that the national average price of diesel fuel slipped 0.3 cents per gallon last week to $1.320, breaking a six-week upward trend.The DOE reported that the price of gasoline also lowered last week, losing 0.9 cents per gallon to end the week at $1.404. According to the report, the average price of diesel fell in three of the DOE’s five geographic regions, the East Coast, the Gulf Coast, and the Midwest. The price on the West Coast was unchanged, and the price rose in the Rocky Mountain region.Diesel fuel is still most expensive on the West Coast, where the price remained steady at $1.405 per gallon. In the Rocky Mountain region, the price rose to $1.357 per gallon. The cheapest diesel fuel was along the Gulf Coast, where it declined 0.6 cents to $1.278 per gallon.