TCAS Change 7.0 or ACAS II was introduced for RVSM - you no longer get "TRAFFIC TRAFFIC" flying past another with 1000 feet separation - the envelope was changed to the region of 700-800 feet.
Plus when 2 aircraft converge - one climbing and another descending the logic in the software would be inclined to give you commands which required the least v/s change i.e. climbing/descending through each others levels - TCAS is not coupled and does not know what the Autopilot is doing i.e. ALT ACQ/ALT *
Good idea to reduce the ROC/ROD approaching cleared levels/altitudes by whatever means.