The 318 LA has a miserably small cam. Many years ago I added a CompCams 260 High Energy cam with excellent results (there are better choices now). Mopar's own "RV" grind is a popular upgrade. My engine maintained the same fuel mileage (19 mpg back when men were men and gas was gas), but power was much better as it'd no longer fall flat above 4,000 rpm or hit a wall in 3rd gear. Any reasonable cam choice will greatly improve overall performance. Just remember to upgrade the valve springs to match that upgraded cam. Otherwise performance suffers and you could scrag a new engine with a dropped valve. Full disclosure-I also had headers and an SP2-P intake (great for mileage).