When I first started playing, I too found my fingers or grip strength very weak.
My hands both left and right got tired very quickly.
I bought the Finger Master and used it a fair bit.
I use it when I am watching TV and when I am laying in bed at night before falling asleep.
Over time, my grip strength does improved but my hands still got tired easily.
Cincy2 wrote:You know what the answer is. Technique, technique, technique. The hardest skill to master in playing is the ability to totally relax and only apply the MINIMUM force needed to play a clean note. I still pursue this objective.
Cincy's advice is the key or answer to your quest.
I gradually realized that I was griping the neck too hard.
Try to fret the note with the minimum amount of force, just enough to make a clean note.
Remember that strength level and practice at that level without applying too much grip.
Also try to use your arm strength when fretting by pulling back a bit (not a lot), just a bit.
This can minimize the thumb grip pressure if you use you arm muscle.
This way, you are not relying on the thumb muscle to do all the work.
Try to dance your fingers on the fret board rather than squeezing the neck (easier said than done).
Technique, technique, technique....
Give yourself time, it will come gradually and eventually.