How do I tell if my 2003 GMC Yukon Denali has econ- boost?

It used to be called Variable Displacement (4-6-8) on the older Cadallic engines. It is now called Active Fuel Management, introduced in 2007..... I think!!.. You can do some online research OR just call a GM dealer with the vehicle ID number to be sure... Pretty sure your 2003 6.0L does not have this feature!