I'm guessing you mean that your upper half is getting out front too early. That's a postural issue. I also agree with leading with the front hip and keeping head and spine slightly behind the front hip into foot plant.
As for stiffening the front leg, it's tough to say without seeing you but I'll suggest speeding up your tempo and keeping the same stride length before shortening your stride. This complements the leading with the front hip. Get the hips going sooner and faster.