RJM -
I assumed that you know this but TestStand does collect results as it goes so if you are running for a long time, the set of results will turn out to be quite large and will consume a lot of memory.
You could verify that the collection of result is your concern if you enable the Disable Results Recording option on the Execution tab of the Station Options dialog box.
The previous suggestion to use the TestStand 3.0 with its on-the-fly report generation or database logging features along with enabling the conserve memory options on the Model Options dialog box is one way to prevent the default TestStand process model from collecting results after they have been processed by the model.
Scott Richardson (NI)
Scott Richardson
https://testeract.com