Increasing your speed can be about more than just numbers on a clock. Getting faster can be about pushing past your perceived boundaries, or feeling the freedom of really letting your legs go. Take your time, stay relaxed, and enjoy the release.
There are times when it feels right to push a little; and when I do, I incorporate appropriate amounts of strength and technique to get the job done. But, every action I take and every adjustment I make needs to contain a certain amount of relaxation for the “pushing” to be efficient and not be met with any resistance.