as far as supporting mods with the tuner, etc
open exhaust if dont have it, at least the cat needs to be gone
you can get by with an SCT not doing anything else but you need to monitor ECT/EOT before oil cooler clogs, leading to a rupture in the EGR cooler, leading to lifting your heads and blowing the gaskets. its a chain reaction for the 'most part' although there have been instances where people say their ECT/EOT deltas were within 5 degrees and blew head gaskets, but those possibly had other issues as well (the gaskets we all know now not to use, heads not flat, etc). Gauges/monitor is the primary mod to go along with a tuner if you dont have the $$$ to just throw studs in at this point as its not cheap. Coolant filter being prob #2 along with an EGR delete. removing some of the beginnings of where it all starts will add some longevity.
but like everyone said, the tune will better supply fuel and if you drive like grandma your mileage will improve, but once feeling that power it becomes VERY difficult to stay out of it
