I am little bit confused with your problems. Perhaps you can tell me the problems in order of action you have done.
Which LAC has been going down for the paging success rate? Is that the New LAC/BSC that you have mentioned before or the other LACs because of the appearing of New LAC?
If your mention is your paging (total) is going down after splitting LAC/BSC, it perhaps you have unsyncron dbase between MSC-BSC(specially New BSC/LAC) Please check the BSC SPC and LAC dbase from the MSC.
But if your mention is your New LAC/BSC’s paging going down, it perhaps because of the transmission. Usually in rural area, the transmission is going flicker in that time (3-8AM), perhaps because of bad weather.
Paging success rate can be rise by setting the paging timer in the MSC