Plateau for 2 years

HI Redditors,

I've been stuck with the same race times and training paces for the most part, and i feel i have been patient in training(let me know otherwise) over the part 2 years. Would like to have your suggestions as to what can i do to break through this Plateau.

Background: 28M, Run between 40Miles - 50Miles/week, 4 years into running.

PBs of 17:2X (5k), 37:2X(10k), 1:25(Half)

These timings have been +/- 15s since 2 years ago, there has not been much progress in race times, and my training paces has not felt like it has improved also. I recently ran a 37:3X(10k) the past month, so i know the level is still around the same.

Weekly training routine(Similar for past 2years):

1 x 30-40mins of Threshold broken up into sets mostly.Eg. 5 x 6mins, 3 x 10mins etc. I've been running about 6:25/mile for about 2years. Have tried going faster occasionally, however the HR just drifts out of control and the effort levels seems to hard for threshold

1 x 20mins~ of Speed work broken up. This is usually done around my 5k-10k pace. Usually its around. Usually ranges from 5:30 - 5:45/mile.

1 x Long run which i would just cap of at 2hours usually.

The remaining days are about fitting in approx 50mins of easy running.

I've also engaged running coach past 2-3 years and found that most of them keeps the same routine which is why i'm quite at a loss of what to do at this point.

Any advice would be appreciated guys.