depending how many miles are on the truck id personally just fix the head and spend the money on a set of headers.. i know the 6.0 had more potential but there isn't much improvement for the time and money hes gonna have to put into it.. he could run one more psi and make up for the difference between the 5.3 and the 6.0 or close to it. fix the head ... cam and headers and a nice tune you'll be cooking .. also think about going up to 4:10s or maybe bigger (depends what you do with the truck) 3:73's are decent ... i just went from 3:23's to 5:13's its nuts to say the least.. I have a t56 tranny though that the only reason i can go that high with the gears (.5 final drive) without slaughtering my mileage. just set it up right and you'll have to change your sig i promise