remfak;
I'll preface my answer with the understanding that we've never run much US diesel through our current rigs, so I can't speak to the specifics of the fuel quality.
We've had a '90 Jetta TDI for 17 years and our current pickup is an '03 Ram with the 305HP/555ft/lb 5.9 L Cummins.
As well, a nephew is a HD mechanic who is trained/certified for Cummins engines among others has been a valued source of information for us regarding our '03.
One thing we do notice up here is that we do get noticeably better fuel mileage once the stations stop using winter diesel. We don't see a lot of bio-diesel here in BC thus far either, so I'm not sure if a higher bio-fuel content might have a positive or negative effect on economy.
In our experience, I'd certainly second or third the recommendation to not go to an oiled gauze air filtration system. We gave K&N filters a try on a 4.6 Ford gas and our Jetta and were not impressed at all. None of the mechanics I've talked to since recommend them, especially so for turbo diesel engines.
A friend in Alberta had a 6.7 that got significantly poorer mileage than his '04 with the 5.9. He replaced the entire cold air intake with a K&N system and reported no change at all in either power or economy.
He then chipped it - Bully Dog I believe - and that did help the mileage.
The central Alberta dealer he dealt with - and btw one sees a pile of diesel pickups in oil country - indicated to him that the '07.5 with the newer engine series weren't expected to get as good fuel economy as the older series....Isn't "progress" wonderful sometimes?
The folks who suggested this sight -http://www.cumminsforum.com/ - were spot on in my experience. Think of it as a Campfire for Cummins enthusiasts and there are a lot of us out here.
I did install a silicone rubber "Cool Hose" on the intake to the turbo - but using the stock air filter. I picked it up from these folks and received very good service from them.
http://www.dieselpowerproducts.com/...-finally-got-them-67l-dodge-cummins.aspxI'd say we picked up about 1 mile per Imperial gallon by installing the Cool Hose and can certainly hear the turbo spooling up a bit quicker. I should note that on our '03 it did increase the amount of turbo whine we can hear in the cab. That doesn't bug me, but might not be welcome for others.
My nephew insisted we run either a Fleet Guard or Dodge oil filter. There was one other one that escapes my memory as well, but according to him all filters are definitely not made equally.
We run an additive in our fuel to help lubricate the pressure pump. We've had no or low sulfur diesel here in Canada for a long time now, so an additive can't hurt I figure. We've been using mostly this stuff and as far as we're aware it's been doing what its supposed to.
http://www.powerservice.com/dk/I'll note that in my research it didn't fare quite as well as some other additives like Amsoil, but because the Diesel Kleen is so easy to find up here it gets the nod.
Based upon a bunch of reading and asking, we use Shell Rotella T in the Cummins, but use Castrol Super Diesel RX in the Jetta - which by the way has 411,000km on it and runs like a proverbial clock. Anyway, I do believe it pays to use a quality oil suited for turbo diesel applications.
I've not added auxiliary filtering yet in either the fuel or the oil, but clean fuel and clean oil can never be considered a bad thing with a turbo diesel.
Sorry for taking so long to spit this all out. Hopefully some of it was some use to you. Good luck with your pickup.
Regards,
Dwayne