Hi,
We have experimented the same problems in the past with CC 60B.
The point is that the maximun capacity of BSU or CCSU is 16 SL per AS7 card but in real it can handle about 12 SL (200 mErl each) with CPU 550. So the best option is to redistributed SL and also ET cards between all Signalling Units you have in MSC. Also it is better to begin a network optimization reducing paging, authentication and TMSI Realloc. load.
Now, using CPU 770 or 816 this CC almost dissapear.