I hope pix agree with me, concerning the signal stregth, check these three things:
VSWR, that NMC didn’t report, may be they thought it is minor!
Second, check your transceiver TRX,and corresponding combiner. it might be software or hardware problems, you may refresh the TRX or Combiner, or even replace them and check!
Third, which is most important, check the power control parameters, perhaps the thresholds and offsetes on this power control window require adjustemnts.
Is this cell a concentric cell with 900 and 1800 (UL and OL), if so it may explain a lot of things too!
concerning the call end issue it might be related to NSS, i need to describe more this call end and what do you mean with any response? check layer three messages during drive test, you might find your answer in these messages.