I have a MC3810 router in remote city connecting Toronto through Serial cable, external DSU/CSU to Frame Relay cloud, we apply VoFR. To ensure voice quality, we use traffic shapping on s0, but there are a lot of traffic shapping output packets drops on pvc and interface, which means there are a lot of packets lost during thransfering. But the cities which have MFT (interal DSU/CSU) connections with same configurations haven't this kind of problem. Today, I made no traffic shapping on that interface, still have a few packets lost, and another city which meets same problem, when I don't apply traffic shapping on s0, there is no packets drops.
Could any Cisco expert tell me how to resolve this problem? I want to keep serial connection and traffic shapping.

Thank you very much!!!!!!!