first you need to look upon other SDCCH Statistc. SDCCH MHT normal values should be around 3-3.5 sec.
if they are normal ones and it is Ericsson system as you state, than go to the OSS and shcedule a CTR recording(PMR and afterward choose recording ot channel level). Maximum time is 1h. After the measurements are finished see in the report menu the statistic gathered for selection types. this will help you identify the reason for SDCCH attempts, and see if something abnormal(The selection types you can find in the ALEX/Channel administration feature).If everything is OK, chek your feeder system. Schedule MRR in the RNO to see the path balance,UL/DL quality ets. Afterwards if TCH trafic is low chek the CHAP setting, and if it is 0 change it to 1.