It depends if it's a Stinger or PowerPack program. The Stinger will add up to 70 HP and 170lb-ft torque and the PowerPack will add up to 100 HP and 230lb-ft torque. It says you can haul in all levels as it's for towing and hauling but you need a Pyrometer.
So, level 1 will be stock and then you have 5 levels. So if it's the PowerPack, it will be 20HP and 46lb-ft torque each level and the Stinger will be 14HP and 34 lb-ft torque each level.
It's a great safe way to add power. Just make sure you get some guages and keep an eye on the EGTs.
As far as the fuel milage goes, Banks will probably say that level 2 is the best all around fuel economy like they said with the 6-Gun I have, but I have found level 4 has the best for my driving and there's another guy on here that has the 6-gun that get's the best milage with level 5. So it will all depend on the way you drive.