Can't trill fast with ring finger, help!

I play Guitar since 2005. I have good trill skills with index finger and (incredible!) with pinky, while ring finger Is totally lazy!! Can't trill fast as the index.

I tried many ways: spider exercises 1-2-3-4 and all variants, including 2-3 and 3-4 exercises. I also tried the classic " keep on trilling with ring finger in one position with increasing Speed till you get tired!", but it seems stuck and really weaker than the others. Can you suggest a different appoach or what helped you to strenghten the ring finger and get fast trills (my goal is Dave Murray style fast trills)?