Congratulations on the new addition to the family. Your in town mileage is what I would expect for a older Chevy truck, especially in town. My older Crew cab long bed Ford F-250 (22 ' long) only does about 10 mpg in town and 13 hwy.
I was asked one time why I didn't purchase a more fuel efficient modern truck. I explained the math to them that the payout would take 300k miles to achieve payout for the upgrade, along with higher taxes and insurance.
I still own my 1999 Ford F-250 single cab Diesel ( the one thieves tried to steal) and it will do 21 mpg on the hwy.
For fuel efficiency I rode my scooters around town so I seen no need to upgrade trucks.
