Are you using Multiband cells?
U may be having a lot of calls on the UL.
Your task is to distribute traffic to to OL.
Check the counters CNRELCONG & CNRELCONGSUB.
This measures the TCH congestion in the OL+ UL & OL respectively.
So the diffrence CNRELCON-CNRELCONSUB gives you calls which cant go through due to congestion on the UL.
This will give you where your congestion is, UL or OL.
The other reason could be that you are experiencing congestion in the transcoders. Check counters TFNRELCONG & TFNRELCONGSUB.
Hope this helps,