When you say "clean of lubricants" do you mean entirely clean? There are several spots in the drawbar / collet setup that should have lubricant, and doing so can increase the holding force by 70%. This is detailed in this whitepaper from Tormach ...
https://www.tormach.com/document_dir...tml?doc_id=163
Also, you should lubricate the threads of the ER nut on the TTS tool holder.