Recent discussion on the radio here in Denver, most diesel is not refined in the US, except in a few locations because of taxes and environmental concerns. Much of it is done in Spain, the crude is shipped there, refined, then shipped back. This came from someone with 30 + yrs in the oil business. Flying J has a facility in SLC for refining diesel that they use at their travel centers in the West.
I've been seeing a lot of road testing in the Denver area and on I-70 in the mountains of diesel equipped Titans with Cummins Engineering on the doors. According to a Cummins rep. for the Class 8 engines that was at our shop, they will be available late 2014 as 2015 models or sometime in 2015 as either 2015's or 2016's. Subject to change, Nissan rep. at the Outdoorsman Expo. said similar when I asked him. I have not seen road testing of diesel equipped Frontiers yet. Where I live in N.E. Denver, I see a lot of road test mules being run up I-76, Ford, Roush (Chrysler, Ford, GM, Dodge), Fiat, Mini, Jeep, MB, Cummins/Roush, Audi (they have a massive facility in Golden, surrounded by 14' concrete walls and two 14' tall gates) all do road testing. The heavily disguised stuff is only road test between 11 pm and 3 am so it's not seen by too many prying eyes. The nice thing about the hours I work (4am to 4 pm), I get to see a lot of this stuff on the road. Many of the current models I've seen in light to heavy camo up to 4 yrs before release.
Also, Cummins, Detroit diesel use a cold storage facility outside Laramie, Wyo. where they do year round extreme cold temp testing. They can bring the temps down to -50 any time of year.