practice the pentatonic scale over and over again...thats what i did to help my self. i had the same problem...i thought my finger was retarded to, then my teacher suggested that. it worked for me and within a week of practicing every day for 30 minutes i was much more coordinated

Well im 38 years old been playing since 77,I always practise on an acoustic after a while it will build strength in all your fingers.
Try playing on an old flattop for 30 mins a day,it will improve you fingering and overall strenth,you can try all the scales you want on an electric,might help some,if you dont have an acoustic,try doing pull offs with that finger over and over,sounds to me your finger is a little weaker than the others.
I hope this helps.

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Tommy Jones