Yep. The kit itself has no effect on MPG. It's the taller tires you'll install now that you can that'll drop your mileage.
Well. it's the Campfire so I'll offer the required disagreement.
All the trucks that are nose down allow air to move over top of the smooth hood, windshield etc. as opposed to going underneath & buffeting around all the off shaped parts of the undercarriage.
Mileage won't likely change more than 1-2 mpg, but the low front is just another trick of the mfr. to try & meet unrealistic gov't mileage standards. A little here & there.