Okay, truck as in the kind you buy from a dealership; F150, F250, etc. These are the trucks I'm talking about.
Do you think they could get a clean diesel engine, like the Jetta, in a sedan? 40 mpg highway?
Honestly, no. Again, to much drag and weight. The trucks can't be geared for full out MPG because they would lose their utility. Benz, BMW and Audi diesels average around 19-22 in their heavy SUV's which is great, but other than a massive decrease in weight and/or drag that's about where the mileage will stay, maybe a bit more, but that's it. The most adv. diesel in development is GM's 4.5L unit that is in flux right now b/c of the bankruptcy but from what I hear and read it is truly a leap in design and efficiency/emissions, when that is released we will see numbers in the mid to upper 20's. IF it's released.
EPA/CAFE/Safety regs force producers to add weight/complexity (meaning price) to cars in the way of emissions gear, stronger/heavier structures, countless safety devices etc etc. The govt. wants more efficient cars but EPA/Safety regs demand heavier and heavier cars which leads to auto makers being farther in the hole every year. Plus all the gear added to engines for emissions saps power AND efficiency. Which means they have to use hybrids/some diesels to cope. This adds a lot to the price of a car. It's a fucking clusters fuck and it doesn't make any sense. It's really shitty ignorant govt. at its finest. And as for your Jetta diesel, it would be far more fuel efficient if it wasn't for the emissions gear needed to make it U.S. spec compliant.
And as for trucks you mentioned above. The Tundra, besides being a truck with many quality issues, gets beaten in comparisons and gets lousy gas mileage. Same for the Nissan Titan. Both trucks also tanked in the market place, total failures. The most efficient truck on the market in terms of MPG would be the Chevy Silverado/GMC Sierra and their hybrid versions as well. And anything above a 1/2 ton can't be included because no Asian automaker has dared to venture into that market segment, for good reason.