You have this. You need an eight beat mantra to focus on. "I will finish, one step at a time" might work for you in this case. Just kind of zen out and focus on those words with each step. If you need to hear someone else's voice consider Blondie's One way or another (
https://www.youtube.com/watch?v=_zBwRDEFMRY) with the words "One foot in front of the other, I'm going to finish, I'm gonna finish finish finish finish finish" It's not perfect but it gets the job done. If you can isolate if it's your legs, your lungs, or your mind that is holding you back in any given moment, turn to Simon and Garfunkel (
https://www.youtube.com/watch?v=z1Reuyu9e_o) and customize for you "slow down, you're going to fast, you have to make those (lungs, legs, mind) of yours last. (Jogging, racing, running) through the Cherry Blossom race (joggiing, racing, running) along and feeling groovy!!!
Pick one song that will push you and put it on when you need to push. I love Bruce Springsteen and one of the best songs he has that is both a driving/pushing song BUT at a very steady even pace can be a metronome.
https://www.youtube.com/watch?v=RJVauHVQ-X0
If you need to feel lifted and energized, his song the Rising also can do that.
Rotate through the above as needed. you got it!