GMC HD2500/HD3500 fuel milage ?

[-JR-]

I am in the process in ordering in a new GMC HD2500 /HD3500 with a 6 L gas engine
The only gear ratio is 4:10
Just wonding if any one has one and what is the Fuel milage is, as dealers have no specs ?

ps Please don't come on saying i am better off buying a diesel.
This truck will be my daily drive to work truck in Edmonton weekends will be pulling my boat with a truck camper
Heavy duty Tech last 30 years.