The stock turbo is restrictive at higher rpm. You will have more power to accelerate up to speed, but can reportedly loose mpg on the highway. especially with 4.11s. So the story goes...
That said my Hummer was n/a with a soft rod knock when I bought it. engine went boom , and in goes a new optimizer long block, rebuilt db2 Ip factory settings, while it was out and used same injectors. SAME MPG. Then a few years later I just put on a gm6 with homemade turbo master, and restricted the exhaust worse than it was after the turbo for the down pipe being 1/2" smaller for about 3' long. put in used turbo injectors with approx. 80,000 miles on them and turned up fuel screw 1/2 turn + to supply the turbo (only needed 1/4 turn for turbo factory settings) and much faster acceleration I can still do same speed highway, but it is more prone to overheating, from higher egts. SAME EXACT MPG. A 4" exhaust will help the restriction some and will drop egt's, I just have not had time yet.
I think it is simply the engine does not have to work as hard to produce the required power to get it up to speed, or to keep it there. If you do a lot of highway driving there is a bit to consider-- maybe different results with your way more aerodynamic and lighter truck? If you keep your rpm at 2200 or under most of the time then it is a no brainer. If you put a ton of miles on it get the ATT, it increases efficiency so much it will pay for itself in fuel savings in no time. I would, I just can't fit it in my rig.
You will need to reset the pop pressure of your injectors, or get different ones for the turbo. If you go n/a, I would question which precups to run.
The belt system does not have to change iirc, not sure, but more torque from the engine could cause more slippage / chirping. A fd balancer would off set that I believe.
I would pick up the arp studs from Leroy instead of buying new tty head bolts. Victor Reinz or Felpro gaskets.
If he doesn't respond here, pm WarWagon this sounds like his favorite world of changes.
Les--3 drums in the bed heck of a suburban...:hihi: