Am I experiencing the garage spike/how to feel a fluid motion?

I'm feeling more stuck in my playing than ever. After 15 years of playing, I still struggle with a staggering, stuttering sensation in my picking hand that I just can’t seem to shake. Years ago, I accepted that I wasn’t a fast player and shifted my focus to reading, theory, improvisation, and composition. I also used the fact that I’m left-handed in everything except guitar as an excuse to further justify my lack of speed. Interestingly, my left hand consistently outperforms my right in motion tests, which isn’t surprising. I play in a band and take pit orchestra gigs when I can, but it’s incredibly frustrating when a song requires higher speeds. I either have to modify my parts or ask to slow down the tempo. My speed maxes out at around 140 BPM when playing 2–3 notes per string, and even then, I often fumble through my lines. At times, I can tremolo pick 16th notes at around 170 BPM, but I have to ramp up to that speed, and even then, my notes sometimes stutter. For years, I told myself that consistent practice would improve my speed, but it hasn’t. I’m at a loss for how to develop a smooth, fluid motion where my pick glides effortlessly over the strings. No matter how much I work on it, I can’t seem to find that natural, glassy feel in my picking hand. Thanks for reading!