With all due respect, I am not convinced you will see 17 mpg out of a 04-08 3/4 ton 4WD Hemi even under your testing conditions, at least not with the 545RFE. There are a small number of MT trucks out there that might do it, but I still doubt it. And if I was to run that test, I would put a full 80 psi in the tires....

I agree that exhaust changes don't make much of a difference. Maybe with the full JBA set up, but the cost would swallow the increased mileage savings such that I doubt you would reach a positive ROI. I have the cat back set up on my 05 QC 4WD Hemi. It is lighter and sounds cool, but that is about it.

The only thing that seems legitimately reported to increase mileage are the hub conversion kits - spyntec, dyna-trac, etc. Again, the cost will far exceed the savings, but there are some other benefits. I am looking at these now.