Dustin, welcome to the forum!
As you might know yourself, there's many parameters involved. Throne balance/height, pedal settings, core strength, practice habits, technique... Your issues are likely the result of one of those parameters or a combination of them.
I think it's crucial to stay relaxed, both physically and mentally. Expel the term 'frustration' from your mind! And always be prepared to think of any progress as a long-term activity.
I've been working on swivel for many months now (and I'm not bad with singles/doubles I think) but that was yet another example of how much effort some things might take to get the hang of them. Recently I've also started working on the hertas (not really a Meshuggah fan here but hertas are simply cool) and it's not easy. (I'm up to 200 bpm, for a few bars - I can play the orig. speed with a different footing though, but also not for too long.) What has been helping me was to not push it too hard, not overfocusing, and to switch between leading with my R vs. L foot quite regularly, every 10 minutes or so. You need to bring your L foot up.
You might have noticed that speeding something up is what your body will do by itself provided you've been practicing the motions correctly and slowly. It just doesn't work overnight so be patient. There will be progress!
A video of how you're typically practicing might help for troubleshooting.
Also, you can use the forum search engine for double bass related stuff like speed, issues, pain etc.
As for pain - you should _never_ have some. Burn is good though. You might want to take up stretching/proper warming up before your double bass practice.
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I recommend reading this thread - it covers 2 of the very best tutorials on foot technique out there.
Best Foot/double bass DVD?