This is one excercise I do for stretching:
Take a Major 7 shape with root on D16, 3rd on G15, 5th on B14 and 7th on e13. Start lowering the notes of the chord by a half step one by one, starting with the 7th and, 5th and so on and sound each chord. Once you reach E1, then go back up. When I first started this, I couldn’t go all the way and needed to reposition my left hand fingers with my right hand. That’s OK, because the idea is to make the stretch and get your muscles to hold the shape. Eventually they will get all the way and you can start worrying about grabbing each note right behind the fret not to pull them sharp and obviously the ultimate goal is to lose the “deathgrip” and do the shifts effortlessy.