Sounds like the usual syncro issue from 4th to 5th...
What sort of budget do you have for the exhaust as we have a few options here - http://cougarstore.co.uk/index.php?main_page=index&cPath=1_10
Please do let us know if we can help...
We can help with new, listed on our site here - http://cougarstore.co.uk/index.php?main_page=product_info&products_id=112&zenid=8120b3e3539c07e35a8b590a2592dcf0