Robert Rønnes has written a great method book called Twelve Virtuoso Studies. I have been working with this book for over a year now and it has been an asset for my technique. This has been especially helpful on contrabassoon and contraforte for down slurs. Excerpts like Elektra have large down slurs that need to be clean AND sound like it’s easy. So the first exercise “Warming Up” is all middle and low range, which isolates large interval slurs. Running through this every day on contra has made a noticeable difference in my playing.