Do you feel like you are falling and out of control and top speed?
Feeling like you are falling probably involves braking. Braking is when the foot contacts the ground as it is moving forward rather than contacting the ground as it is moving backward. This could be the result of several different inefficiencies:
The thigh is not in a position to use the glutes.
One cause might be that the thigh is not rotating forward fast enough to have time to accelerate the foot backward with the glutes. This could be related to the trail leg being passive after it leaves the ground. This may occur in the hamstring and/or in the hip flexor. The hamstring could be passive which leaves the leg long and slow preventing it from rotating quickly. The hip flexor could be passive which also prevents the leg from rotating quickly. If either or both of these problems are corrected the thigh should be able to rotate to a position close to 90 degrees from vertical and stretch the glutes. Then the glutes will have the time and the range of motion to accelerate the leg and foot before contacting the ground.
The thigh is in a good position but the glutes are passive.
Unfortunately, even if the thigh rotates fast enough, the glutes probably won’t be automatically engaged. It might take a few weeks of focusing on using the glutes to develop the timing to start to use them effectively. Activating the glutes and rotating the thigh down and back will accelerate the foot before contacting the ground so that it can pull on the ground rather than braking.
Another approach to correcting the problem of feeling out of control at top speed is to think of scissoring which is a combination of the two above movements. This will coordinate the glutes, and the hip flexor of the opposite leg, to begin bringing the legs together before ground contact. The foot will contact the ground while pulling backward, the knee of the trail leg will be moving past the other knee, and the thigh will be able to rotate forward before the next stride.