Does trunk group page 2 of your R6 switch have a field like this: US NI Delayed Calling Name Update? n
For National ISDN CNAM to work this usually needs to be set to Y. This is because the LEC sends your call setup message right away when you have an incoming call, while the LEC switch is doing the CNAM database lookup. After it gets the response to the query it sends the name in a subsequent message, and the Definity must be ready to receive this and update ringing stations.