as you know that PCU2_d can handle 256 channels (16kbps) the utilization should be 70% that means 180 channels so your calculation as:
=no of sites *no. of cells *CDEF*(channels support GPRS in TRXs)+EDAP channels (16kbps)
for example in your case
S3/3/3 :all TRXs enabled GPRS and channels =3*8-BCCH-2SDCCH=24-1-2=21
so we have 21 channels in TRXs enabled GPRS per cell and we have 3 EDAP timeslots (64Kbps)=4 (16kbps)*3=12
so per site
21*.34*3+12=33
1 pcu can handle sites
=180/33=5 sites
NOTE:i recommend to increase EDAP to 6 timesloats