you probably have something out of whack on the tune-up or there could be multiple issues. i'm not a holley hater and a 3310 can be made reliable and reasonably economical, but if it was mine and efficient driving is critical i'd seriously look at an edelbrock 650avs. the 650avs is nearly identical in size to an original factory 383 avs which means it will have smaller primaries to drive on which will be more efficient. holley's in general aren't the best choice for good mileage but can be made to work. make sure your vacuum advance is working too. a working vacuum advance will aid in good driving and fuel mileage.