well idk how the trannys are in the 04+ but thats a big one for us 97-03 guys.. mod as in the power adding aftermarked parts.. a t-stat or intake or somthing like that isnt going to be a bad thing, the "bigger" gofaster parts can bring the motor life down though is what i think he is trying to say.. roller rockers, cam, im not sure what exactly the n/a guys do but i think thats wehre this was headed