2bl does NOT mean less gas.
In fact if you have 2bl and 4bl same cfm, the 4bl will get better milage because during cruseing it is running only on the primarys
a few more tricks to get better milage are
1. Dont accelrate hard
2. Keep your truck tuned up and clean filters
3. Check your tire pressure
4. Using A tachometer and watching your rpms can also help you keep track of how hard you push your engine
