Took my S2 for a spin as she's not been out for a good few weeks. The old girl is running sweet and sounds lovely

Unfortunately it doesn't seem to be making its power. The boost guage soon whips up to the 25psi but it just doesn't seem to be going. It just feels like a N/A car then at 4000-4500rpm it goes a bit. Just feels really flat though.

Any ideas?