if i go the truck ls1 i will just use the 4.8 i have and then latter get a 408 block to replace the 4.8 block. right now i just need power and good mileage. i already know that the 6.0 doesn't get great mileage, my grandpa's truck never gets better than 16 on the highway. even my 350 could pull that kind of mileage, not as much power but still. the 4.8 gets 18-22 mpg on the highway. but if anyone has any more suggestions keep them coming, i really do appreciate all the impute and advice, since i still haven't made any set decisions, if anyone has a suggestion on another engine to use you may be able to change my mind.