Remember just because the 6.4L gets poor mileage stock, you can buy alot of diesel for a 15k difference in buying a truck, based on a 5 mpg difference (6.7 vs. 6.4)
So based on a 6.4 getting 14 and a 6.7 getting 19, with diesel $3.50 a gallon it costs you $65.78 more per 1000 miles to drive a 6.4 over a 6.7. You can drive a 6.4 alot of miles to recover the $15,000 price difference. Which should be ~228,000 miles.
@ $4.50 a gallon its $84.58 per 1000 miles, or a total of 177,333 miles.
I hope that made sence 
Here's another option, DPF delete with a Gryphon will get you closer to the 19mpg the 6.7 makes. I don't have a a 6.4, I hear 17+ is not out of the question.
__________________
19 F-350 6.7 Auto
16 F-350 6.7 Auto
05 Excursion 6.0, Auto, PHP Atlas 40 FICM, ARP Studs VXBC6(truck PCM)
00 F-350 7.3, 12 Speed, PHP Gryphon, PHP hydra, DAC3
95 F-Superduty 7.3 DI, Auto, Mechanics Truck
94 F-Superduty 7.3 DI, 5 speed, Flatbed
|