How much mpg you get from injector change has much more to do with the current condition of your injectors then what the new ones are. How well your injectors are has everything to do with mileage, oil change frequency, fuel filter brand and change frequency.
The things that will have a significant effect many times are ones that effect looks and therefore people are less quick to make them. Narrower tires pumped up to max pressure, light wheels, smaller side mirrors, lowering trucks stance especially the front, Bed cover, anything that can drop weight. If you do mainly hwy driving going to 3.55 gears.
For hwy a looser turbine housing or even larger over all turbo as the lower boost @ cruise the lower the drive pressure the less engine drag. Take a look at some of the mpg of trucks running large turbos and even large injectors. They are as good as a number of full stock trucks.
Learning how to drive for maximum mpg. Its very different than the way most drive. Timing your stops using the brake as little as possible. Coasting as much as possible. Timing and building speed when coming to hills. Taking off as slow as possible when from a stop will have a huge effect with city driving.
Do not let your truck sit and idle. The second its started and the idle has stabilized drive it. Do so super easy but drive it. The faster it warms up the better. A truck idling will take forever to get to anything close to full operating temp. All that time burning fuel and not doing a bit of productive work nor helping the engine in anyway either.
Low back pressure on the turbo, single shot injectors, good oil pressure and quality, driving style, weight, tire size, and good tuning.
