1/are the drops occuring in GPRS or in EGDGE ?
2/ are they occuring at any time of the day (proportionally to traffic), or are they especially located around the busiest hours of the day?
3/ reduce the maximum MCS possible from MCS9 to MCS7 *and* from CS4 to CS3.
4/ try pushing the GPRS allocation to another TRX (right now, either your GPRS is going on BCCH trx or it is not.. whatever you have chosen until now –> do the opposite)
You may also suspect a BSC issue ? In such case, you might consider doing a BSC “gprs module” restart during the night. Have you already contacted your technical support, check if there isn’t any bug in the software release you are using ?
If nothing worked, then it’s gonna be complicated to help you remotely. There are several things one can do, but that requires heavy analysis.