if you don’t see anyting abnormal during drivetest, i would suspect a customer problem… could you check
– dl tbf congestion ?
– dl tbf throughput ? (not per cell, but per tbf)
– anything related to DL gprs activity : llc volume ? tbf avg duration ? volume per DL TBF ?
it might be that you have only very very little gprs traffic in that cell therefore you have statistically a lot of chance of seeing gprs signalling for MS with poor radio quality.
also, what is the DL RLC retransmission rate ?