Fuel mileage still sucks

[Rawze]

Doser injector seeping fuel into the exhaust?

could be how its driven, how fast you go, or somethng actually wrong somewhere that you have not found.

I know at 4 mpg, I would have gone out of business.

You might also want to mention what make/model truck, engine, some other history, etc.

Is it de-mandated?.. if so, who's programming?... what hardware mods have been done?.. etc.etc. also helps to know too.

There are 10,000+ things that can effect fuel mileage. The driver being the biggest influence of them all. Could also be engine or truck related too, however your question is also very vague with what might be going on.