Had the same problem- very low to almost non-existent knee lift, very little back kick. Shuffled along. Was causing some chronic injuries because of this. Went to get my gait analyzed and came away with 3 very big points:
1- think more about raising your heels upon push off. At first it felt like I was almost prancing on my runs, it was really awkward feeling and I would tire out after about 1/2 mile at first (even at a slow pace).
2- Core strength- not just sit ups and planks, but dynamic core strength. This also ties in with correct posture. The way I was standing and sitting was increasing the strain on my hamstrings and low back and in turn increasing the tightness in my hip flexors which in turn was making me run with little hip motion.
3- Strengthening your extensor muscles- meaning glutes, hamstrings, calves, etc. My quads and hip flexors are strong but my glut medius and hamstrings are weak. Glut medius produces a ton of power for your stride. The one major thing that I have changed is adding in the hip machine and hamstring curls 3-4x per week and I can tell a difference in my stride. I feel more opened up and like I am actually getting use out of my butt and hamstrings.
I could go on forever about this but if you have any more questions let me know.