Contact user STED9r. He keeps a fleet of 6 liters on the road.
Its a job!!!!! No, really, its a job.........
Don't ditch the egr cooler, take that stash of diesel power and what ever other magazines your reading and burn them.
The egr, as much as later models have issues, serves a rather important job aside from emissions, it keeps your combustion temps in check which saves motors in mote ways than just temps. Lets not even go into towing and I'll just assume a pavement pounder so I'm not tapping out with one finger a 2800 worded dissertation how that egr valve is saving your ass when your towing.
The 2003 are good coolers, they're round tube, round hsng coolers. Changed to flat fin square hsng in 2005 1/4 and replacement for those to get the good round tube cooler is from bullet proof.
Keep the egr valve clean along with ait2 which is the temp sensor in the intake about 6" away from egr valve on right side.
Not trying to be an obstinate ass, just get my panties in a bunch on an occasion.
Fuel mileage? Anything from 12-16 in town is good and hitting up around 20 on freeway is good.
Keep oil changed, not by huffy lube, Midas, oil can Henry etc. Use good oil, syn isn't necessary but blend is good and regardless what "good" oil your using dump at 5000 miles. Keep your fuel filters changed, the 03' injectors do not like getting starved for fuel and updating the fuel press reg spring is good.
Might want to have a dealer pull down the turbo and clean actuator ring so the turbo functions properly.
I'll be bluntly honest, the 6.0 is not for the meagerly mechanically inclined or the ones that save money by stretching out maintenance an going on the cheap, or the ones sitting on the crapper getting 6.0 educated by some diesel magazine that's sole purpose is to make money by selling advertisers products. I've been doing this for 32 years, if I count tearing apart my parents cars, appliances and flipping broke motorcycles as a kid, add that up to about 37-8 years. I'm by no stretch what I would consider an expert wrench even with a book full of ASE certs(that says master), 1000 of hours of various training and reading. What am I saying here? The 6.0 should be maintained and or repaired by someone that knows the vehicle.
Don't slap "tuners, chips or power adders" to something just because the diesel rag or so an so says so. Hell, I could go into the programming issues within the pcm when various components of that mtr doesn't read what it should and adjust fuel curves, timing etc all day long.
Keep the egr valve clean and get her out and open up the throttle on an occassion..........