You say that you practised with a metronome for 37 years [!!!!]
You also say, regularly, that you are "firing" your i, [m or a] finger "too early" and have now fixed your problems by ceasing to do so.
Firstly, what does "firing" your finger mean, in simple terms? Secondly, if it simply means plucking the string at the right time then I have to suggest to you that achieving that aim is precisely what slow practice, with a metronome, is guaranteed to fix - provided, of course, that you listen carefully and push through the string at the precise moment the metronome clicks.
If you would just allow yourself to play open string exercises at around 84 bpm, playing p a m i individually on each click - and video yourself doing so in a way that allows people following your thread to see all three fingers and thumb as they pluck their respective strings, then that would be very useful for all of us.
I have a sense that you won't do so, though I don't really understand why.