Are you using TC-NX integration?
How are you adding the STP files to the item revision in Teamcenter, as a separate dataset?
I am certain about the DXF,DWG,UGMASTER,UGAPRT,PDF preview, but not about STP (or STEP).
When you import some dataset in TC, option 'Tool Used' shows the tool for that particular dataset.
UGMASTER/UGPART - UGII V10-BASE
Bitmap - PV
Word file - MSWord
PDF - PDF-Tool etc.
I am wondering the tool to be used (if it is available) to import it directly. In my case when I import it using 'Ctrl+D' > Select the STP file from OS location, it's showing tool used as 'CAE_Dummy' which seems to be incorrect.
If I drag and drop STP file to item revision, it does get added. When checked under named reference there is nothing to show, it's empty. Can you check the same? I am doubtful about the preview of the STP file format in TC.
EDIT: Preferences need to set for the dataset to view in the viewer
<dataset type>.<viewer type>=<list of named references>
For example, to show PDF, UGMASTER and UGPART datasets the following preferences can be used
STEP (*.stp or *.step) files are not supported for viewing in the embedded viewer in Teamcenter . With the correct TcVis license the STEP file can be opened in standalone TcVis.