One thing to keep in mind is that 32nd notes and Sextuplets are nothing more than 16th notes and triplets played twice as fast.
If you slow things down enough, the 32nd notes will sound like 16th notes, etc. It's all subjective ... so don't be intimidated by them. See them for what they really are and work on them using the suggestions every has given you.
If you can't play them
clean at a slower tempo, then they will sound even worse at faster speeds. Don't fool yourself into thinking otherwise. Slow, deliberate practice is THE way to master these rudiments.
Just to reword what has already been said, playing
check patterns or
skeleton figures is a great way to gain control over the rolls, making sure you don't rush or drag. An example of how you might do this would be to play one measure of sixteenth-notes, followed by measure of 32nd-note roll. You are just diddling the 16th notes, which makes it sound twice as fast. The same goes for the sextuplets; play a bar of triplets just before you go into the sextuplet roll.
Pick up these books:
- Stick Control by George Stone
- Developing Dexterity by Mitchell Peters