Hi Suzi
Pls check if you have given high (1)trx priority for TRX 1 i.e. BCCH. If yes, then make it low (5)for some cells and then observe the downlink quality.. You can also do the same excercise each TRX wise within problemetic cell, It will help you in detecting if the problem is with Hardware/Freq.
Other Solution is to check your Handover / Power Control parameters. Check the parameters for Rapid Power Control and downlink quality handover algorithm parameters.