6.0 is the way to go. with the low compression lq4 u can turn that boost up, and the extra displacement just adds to what u already have. theres no substitute for displacement, and the way the 6.0's r going might as well just swap it straight in. idk a cheaper way to gain hp, maybe a tune but thats it. u can find 6.0's for less than 2 grand, idk what else u could add for less than that with that big of an upside.