i'm currently using a Cisco 7206 NPE-G2 with a PA-A3 to terminate DSL customers. i have 6 VP configured with many VC's inside, one for each customer. I used the "atm pvp" configuration specifying the PCR with values given by our ISP. So all the VC's are UBR without particular parameters. We have also a contractualized SCR with the ISP on every VP.
On two of that VP's i have a strange problem: their traffic is well below half of the PCR (even below SCR) and customer reports that their DSL is very slow. If i change the PCR value, for example 3/4 or less of the total PCR the traffic increase and the customers benefit from it. When i put back to real PCR the traffic drops and stay low.
What's the issue with that? The ISP says that everything is ok by their side.
So it may be that someway you are exceeding some CR while it doesn't happen with a lower PCR on the PVP.
As mentioned above, PA-A3 doesn't support hierarchical shaping, for that you need to front-end an LS1010 that is able to do that.