Slowness running TypeMock

We have a suite of several hundered unit tests and are thinking about using TypeMock. After simply enabling mocking, the tests starting taking about 3-5 times as long to run as before. Then enabling fast mode brought the run times down to just a hair over what they were before. Afterwards we started by mocking one of our classes and the execution time was back up to 2-3 times its original length.

We do have a lot of GUI related tests and I saw on the forum that another user was seeing performance issues with DevExpress which we also use. When we only run non-GUI tests, the slowdown is negligible.

Do you have any suggestions for speeding up the tests?

Thanks,
Adam