So after 14 hours and 930 miles behind the wheel, some notes:
Drone: the worst seems to be right at 1600 rpms, between 56-59mph. It does not resonate the cab, nor is it outright "deaf'ning", but you can definitely hear it when pulling a grade at the rpm/speed. I like the exhaust note so much I can deal with it. If you are going down hill at that speed or rpm it's not really noticeable. Any rpm less or more and it nearly disappears. Keep in mind I have the BT gears.
Rasp/CIS: None that I have heard. There is a very slight bit of rasp when the truck is cold when your first start it up at that "light off" moment, but that's it. After a couple minutes when the exhaust is warm, then is none. Just a nice low level rumble.
Interstate driving: Driving with the cruise set above 70mph, the truck actually seems "quieter" in the cab than when stock. Weird I know, but you just hear this perfect rumble of exhaust (very mild, not annoying) and that's it. Before with the stock configuration, you would hear the factory intake "dull roar" more than anything. On my truck, the IJEN and Catless B-Pipes seem to have the perfect "balance" of frequencies at highway driving, in that bad resonance frequencies are either getting cancelled out or are no longer being produced. Lower speeds you hear more of the exhaust, and when accelerating without a downshift you hear a very nice balance of intake and exhaust. Full throttle yields a glorious, "angry" 5.6 liter VK56DE wanting to put the hurt on something or somebody:big_grin: Again, no CIS and annoyingly "bad" sounds heard. To me, "bad" sounds = "cheap" sounds. Think 1980's small block Chevy with duals from mainfolds back running glasspacks and 2 inch crush bent aluminium pipe for my definition of "bad" sounds.
Fuel Mileage: I have checked my gallons used vs. the miles I've driven. No change. I still average close to 14 or so in town (summer it can be as high as 16) and anywhere from 15 to 19 on the highway, just depends on how fast or slow I am driving. So with the IJEN and Cajun pipes, while I may not have increased fuel mileage (is that really even possible on this truck anyways?) there has been a nice power increase and therefore I feel the truck is more efficient with the fuel it does burn. I was not looking to increase it, as I have been impressed with what it has gotten since I bought it compared to my fuel use experiences based off my 2014 PRO-4X. The best it could do was 12 in town and 15 and change on the highway. So my 2015 PRO-4X exceeded my expectations from the get go.
Overall I am very, VERY pleased with this setup. The truck is very responsive, makes great sounds, and is really fun to drive.
Side note: Is it just me, or is the BT gears the greatest thing ever made for interstate driving? If I wanted to accelerate from, say 65mph to 75mph, 80mph or even more, all I had to do was just sqeeeeeze the throttle. Not downshifting, no torque converter unlocking, the truck would just go. It was fairly impressive actually. The other cool part was, since aerodynamically the Titan is about as efficient as a Blimp Hanger, if I wanted to slow down, even in kind of a hurry from higher speeds, all I had to do was lift throttle. It was like applying the brakes. Guess that's where all the fuel goes when you drive a truck that prefers to "ram" or go toe to toe with the wind above any speed higher than 45mph:big_grin: