Ced,
Are you lacking explosive power? At 6 ft and 140 you may need to increase your strength. It sounds like your SSC is good , but you lack the power to get out of the hole. If you don’t have the power to get in the proper position at the beginnning, you get incomplete hip extension. You could be overstriding in the beginning. You may need to rehearse your starts over and over. Sometimes it helps to exagerate the starts by using short choppy strides. By doing this, you will probably stride longer than the choppy steps you rehearsed, but shorter than your normal stride. Look at the CFTS for hints as to lifts. Deadlifts, reverse leg press(glute ham extension), and other hip extension lifts may be most beneficial. Hope it helps.
By adding weight training, you’re already addressing the issue of the first 10. Don’t look for too many other changes till the response to the weights has a chance to take hold.
I have found that weight work is highly applicable to the first 10 or 20.
Do your heavy squats to parallel or below and cleans and snatches. If I can’t make it to the track (because of weather, injuries, travel, whatever…) but keep up these lifts, then I find that my start and initial acceleration are usually right on mark, however once the distance stretches out, then I can feel the impact of missing my speed work.