I'd have to see you run to decide if you actually need this, but increasing your cadence/turn over really helps in increasing short distance speed. I had a running back who was preparing for the NFL combine, and I got his 40 time 2 tenths of a second after simply explaining to him to work on increasing his cadence. He was a great 800m runner to begin with, so I can't take credit for his natural ability, but after I directed his focus towards increasing his foot speed rather than pushing off harder, he made great progress in just 2 months. Unfortunately, his hamstring tore from a car accident... but simply incredible to see an athlete work at that level.
As for the college player, working his power clean turned out to be the fix. He was just too slow off the line, and took too long to get moving. Running with resistance really improved his speed.
I like your sprint intervals. I had my college player sprint short distances and jog or walk back to simulate the pace of a hurry up offense. I think you're on the right track, but if you're good at self coaching, you may want to consider either working on increasing your cadence or adding resistance.
A good running coach is very hard to find, but invaluable if you know one.