first of all You ought to check the reason byond SDCCH congestion if it h/w problem or not.
AND check the following limitation:
# air interface(limmited SDCCH resources)
#A interface (limited # 7 signaling resourse).
# BSC (limited prossesor capacity)
# MSC (limited HLR capacity).
Ericsson have (adaptive configuration for SDCCH and Direct assignment on TCH) so they may help according to your needs.