Perhaps the terminology differs between companies, but in my experience TPM means technical program manager. For large projects they were responsible for creating project Gantt charts, identify blockers early, and essentially "greasing the wheels" between disparate teams.

Again, IMO the good ones added a lot of value by making sure no balls got dropped, which is easy to do with large, multi-team projects. Most of them, though, did a lot of just "status checks" and meeting updates.