2002 Ford Ranger low gas mileage

the truck was still under warranty when i brought it in.It would run bad once in a while so I asked them to check it out.They said I had to replace the injectors.I went to another web site and they told me the following.
1)Check to see if battery was disconnected so the computer can adjust to new injectors.
2)Injector(s) might be leaking.I need to have feul pressure leakdown test down to see if I have leaky injestor(s).
what other things should I check for low gas mileage?

I havent had any modifications or work done on the the truck since the injectors installed.But its been more than 12 months.I had a company van I used most of the time and only drove the truck short distances on the weekends.I will talk to the dealer
and see what they say.
Thanks