Be careful
My Nephew did the tuner thing and had some other work done that required stronger head bolts.

With all that, his truck would role cole and he could tune the FT/LBs over 800.

The sad story was he voided the warranty and blew the motor.

I have a 15 Duramax (LML, the new Duramax is a L5P) that I deleted (DPF only) a little over a year ago. I didn't delete it to roll coal or anything like that. At 40,000 miles my DEF tank heater went out, warranty covered the cost to replace it. At 82,000 miles my DEF tank heater went out again, warranty was up at 75,000. Cost to have the DEF tank heater replaced was around $1,200 and the pattern I was able to apply to my truck, it was going to go out again at 120,000 miles. Buying a new heater and installing it myself was still like $750 and you had to remove the DEF tank to change the heating element.

I decided if I was removing the DEF tank, I wasn't putting it back on. $750 went a long ways towards buying a tune that deleted the DPF and a 5" exhaust. Now my truck runs better, gets better mileage, I don't have to refill the DEF every 5,000 miles. Before deleting my truck, every check engine light I had or issue I had was due to the emissions [censored] on the truck. Does my truck "roal coal?" Yea, if I stand on it, it will. But normal driving you wouldn't know it was deleted.

Mileage wise, I typically see 23 mpg or so driving to downtown Houston every day. On the highway, if I would slow down to 70, 25-26 mpg is very achievable. Coming back from Florida a year ago, I got 21 MPG doing 85.