thanks for all these values, that’s great.
your path balance has a very very bad value (what about path balance value per TRX ?), it shows that your TMA is working too good : your coverage is strongly downlink limited. You might have a problem on your Tx path (your Rx is 17dB better than your Tx)
Therefore, a MS might be able to send a Channel Request on the RACH (UL), but it is unable to hear the Immediate Assignment. It is indeed a readio problem, a real one. Changing the timer T3101 will not help. (you can check with drive tests).
the “1800 MS” problem is not here anymore, as far as i know, i’ll check it out.
your SDCCH assignment failure rate is a bit high (10 to 15% is not critical, but above 10% in an urban area might indicate a problem), yet your overall QoS is fine.
50 to 60 SDCCH assign failures per hour is an absolute number, you got to divide it by the number of SDCCH requests (MC04+MC148 = about 600)
Next step : check if path balance is on both TRXs, or just one.
try locking the BCCH TRX, in order to relocate the BCCH on the second TRX, if it has a good path bal.