A question about your Service Control implementation: when the Service Control dialogue ends for a particular call, is the IVR sending trunk and trunk group information back to the ICM? As I recall, in my last Service Control implementation, the updates to the trunk real-time data were in the ten-second range, and we didn't need to set any Reg keys to do it.
Double-check your VRUCAP logs at the VRU PIM side to ensure that the trunking information is being included when the Service Control dialogue ends for a particular call.