According to "Persistence Modeling for Assessing Marketing Strategy Performance" (http://repub.eur.nl/publications/index/573204148/) persistence modeling is a multi-step process.
The authors of the paper suggest that "unit-root tests are used to determine whether or not the different variables are stable or evolving. In case several of the variables are found to have a unit root, one subsequently tests for cointegration. Depending on the outcome of these two preliminary steps, one estimates a Vector-AutoRegressive (VAR) model in the levels, in the differences, or in error-correction format. Finally, the parameter estimates from this VAR model are used to derive Impulse Response Functions (IRFs), from which various summary statistics on the short- and-long-run dynamics of the system can be derived."
As such I think you will need to use the following SAS/ETS procedures: AUTOREG and VARMAX.
Hope this makes sense,