Buddy I have seen multiple references in some of your posts to excessive noise with ATT, I live & work in the city, have not yet had one complaint about noise, gassers with aftermarket mufflers/exhaust are far more noisy than mine with a Heath exhaust. If I romp on it and open it up yes it's far more throaty than a stock GM turbo/exhaust combo but no unbearibly so.
Now I do have some hearing loss from years around turbines & other large machinery so maybe that is why I'm not bothered, but my burb has same set up at my truck and my wife who drives it does not complain about excessive noise, our pastor does not make note of it when I pull up to the church when day care, sunday school or church services are is in session.
Is your Aero-Turbine 440 muffler which is listed in your signature the source of the extra nosie you are reporting out on, multiple ATT owners are not reporting noise issues, which IMO is a important data point as exhaust type does matter with ATT; as you & both can attest Bank's exhaust is not to be used with the ATT, possibly Aero-Turbine is not as "noise-friendly" as one might need.
As far as mpg with the IC, I never noticed any significant gain in mpg with the IC with either the GM turbo or the ATT, more power with IC but not mpg. The ATT has upped my mpg 1-3 mpg depending how hard & fast I drive, in this case I'd say sell the IC and old turbo, he says he's not going to be hauling much, so probably he's 3:73 as a 2500 (540s10 update sig with more info please) which gives good towing ratio & mpg for his needs.
10 psi boost will get him to 100 mph running empty IAT on most days does not really get hot until running 10+ boost depending what is behind the truck without IC he'll drive a little slower but still should be able to maintain 65-70 without an IC even on hills, or add in WMI a bought or home built kit.
So IMO and opinion is what is being asked I think, in long run bang for buck is ATT, take some of the mpg savings and get a reflash, KOJO tune tweaked for ATT use looks very promising. FWIW member Buck-Buck tows daily 30k# of pipe loads on average, with ATT no IC in South Louisiana 90+F summer temps, no reflash, dually 4500 series truck in oil fields 4:63 ratio IIRC.
Now an unknown is the gear vendors with ATT, nobody has tried that, so possibly with such low gearing with a GV the GM turbo may be preferable as it will have slight edge in lower rpm, so that is a whole new configuration that hasn't been evaluated yet. If you go ATT with the GV keep good notes as I'm considering this myself.
I'd also surmise a GV with the 6.2 would be all one would need, think about the many cube vans, trucks, etc. with 6.2 that are able to do economical work with the right gearing, such as a GV would bring to the table.
