This will come with time. Good advice here splitting fast passages up into segments master the segments and try to do longer segments. Take breaks when you feel fatigued, hit it again.
Digging in isn't bad it is great for accents or dynamics but practice somewhat of a lighter touch to accentuate the best tone, have the best ergonomics, use the lest energy, and control dynamics. These are very important in finger playing and will come in handy when doing accents, different muting, and ghost notes and playing with dynamics.
Playing super fast for long periods of time took years to play some stuff like brutal tech death at 240 bpm for 35 to 45 minutes straight thru a set. I accomplished that by using all four fingers and using both sides of all four fingers to conserve energy. Took years to develop rudiments and string skiping technique, strength for accents, and endurance. The pay off was immense and now I can reach very fast speeds for long periods of time. It all depends on where your goals are for speed and endurance. I played many different genres using 4 fingers for probably about 3 or 4 years before attempting the type of metal I was introunced to about 5 years ago. Recently over the past year I have incorporated floating thumb into all of my right hand finger technique and it also has contributed immensely to my playing as I play 6 string fretless as my main instrument muting is very very important when you play lots of fast stuff using erb basses.
The weirdest thing was getting used to patterns with 4 finger plucking without thinking about it too much. That's when I made rudiment charts for finger order and also for string skipping. Helped quite a bit.
The point of all my ramblings is true endurance will come with time playing with people, playing gigs, and most of all challenging yourself. Focus on technique, theory, playing with people, writing, and transcribing what you can. the endurance will just show up at your doorstep one day and you will be pleasantly surprised.
Lastly a good setup will open up your true potential to hone this technique and endurance. When you know what you like you develop your feel and learn your own economy of motion and know how much strength to use for playing certain things.