Transport Topics has a nice summary of where truckmakers stand on what will need to be done to meet the 2014/2017 emissions/economy regulations
Basically, it looks like the first stage of the phase-in will consist of incremental enhancements to engine accessories and aerodynamics. Think “smart” cooling fans, more efficient electronic components and pumps, optimized aero fairings, etc. The later stages of the phase-in are where the true investment will be needed. Body redesigns may be needed to meet the fuel economy standards, and I’m assuming more extensive engine changes may be necessary as well.

Impact to the new and used truck markets? None of these changes will be free. At this point, it looks like engine technology will not change appreciably at first, so “fear of new technology” should be limited. However, even incremental changes generally carry a price premium, and don’t forget about the aero enhancements. So moderate price increases are likely. Then, as the full 2017 standards are met, the more extensive styling and engine changes should result in more substantial price increases.

The past decade has seen three “pre-buys” as buyers looked to avoid new powertrain technology and its attendant cost. One difference with this upcoming round is buyers will essentially be guaranteed higher fuel economy. The magnitude of a pre-buy will be defined by the premium buyers place on that higher fuel economy.