Gas mileage and boost poll

My daily driver is a 3500 Chevy quad cab dually with an 8.1 vortec big block and an Allison 5 speed auto. Bought it new and put 200k miles on it before turbocharging it. For those 200k it averaged 12.1mpg. It now has 610k miles on it and for the last 400k (turbocharged) it’s averaged 14.6mpg. I record mileage every fill up and have since the beginning. On a long trip I’ve seen as much as 18mpg and if I’m hammering on it, which I do a lot, I’ve seen as low as 6mpg on a tank. With the turbo the mileage is better when you baby it and way worse when you hammer on it. 110lb injectors flow a lot of fuel.