From 2003 owners manual... "Some transmission fluids may be labeled as dual usage, such as MERCON and MERCON V. These dual usage fluids are not to be used in an automatic transmission that requ...
Call a dealer service department. I can tell you that GM switched to Dexron VI in 2006 and its backward compatible with older transmissions. In fact its recommended. If you take a pre-2006 to a GM dealer for any transmission work or maintenance they will use Dex VI.
I would imagine that its the same for Mercon V, but it sounds like the label is clear as mud.