It depends. If you are running a pre-2007 engine, you can use the same API CI-4 Plus heavy duty engine oil as you use today. However, if you have purchased a new engine - 2007 or newer - equipped with an EGR engine, Diesel Particulate Filter and running ULSD, the required heavy duty engine oil is an API CJ-4 heavy duty motor oil.
Please see the following for additional information and FAQs about the new API CJ-4 engine oil.
Chevron Delo® 400 LE™ SAE 15W-40 (API CJ-4)
Texaco URSA® Premium TDX EC™ SAE 15W-40 (API CJ-4)