What does it mean if I can't keep my upper back straight ?

That actually doesn’t make any sense at all, but continue.

If you didnt know, he is like Dunk Champ something like 3yrs in a row!
Im not saying the glutes n hammies are taken completly out of the picture, its just the Quads start doing too much of the work. His hips appear rotated too much also, bringing Quads into action more.
Its hard to tell on his video, however, he is not getting Full Hip involvement - Esp after viewing some footage taken only 1wk ago! Really good hip drive.
Without doubt, he is tight (esp comparing his last wks video, which isnt here) and also Mentally thinking too much which has been stated.
Once you loosen up Silencer, and get back to how you were feeling just 1wk ago, SWEET :). Are you due for a de-load wk yet??
The video posted (at the start) should be forgotten about, and the one from last wk should be Looked at as being Fantastic.
And compare that with Last yrs running form! The difference is like night and day. Even the footage you put up here is light yrs better than last yrs!
Your going to have a good season.

He isn’t running 100% in the video you analyzed and most of your analysis here doesn’t line-up with the video or research. I’ll post more if necessary, but it has been covered ad naseum here and elsewhere.