I am not sure what you mean by “pressure” spurs, but I can tell you that if your legs are not still and quiet, any kind of spur will create more problems than solve – no matter how “strong” your legs are. I agree with the other answer: if you know the horse isn’t lazy, work on conditioning. Take yourself out for a 5-mile run. Imagine someone on your back and prodding you because you have got tired and are not working fast enough.
Take the horse out of the arena and trail ride, if you can. Forget the “training” and have fun with him – likely this will also help you find better legs. Spend some time feeling how the horse’s body moves. When you are in the ring, you can even close your eyes. Feel how his body sways at the walk, and try enunciating its movement by using that leg, i.e. when the body sways to the right, push it over more with your left leg, and when it swings to the left, push it over more with your right leg. In this way, you are asking the hind legs to step up at the most opportune time.
When you post, try squeezing with both legs as you sit – or if he has a sudden spurt of speed, keep posting, but close you hands as you sit, and release immediately. These are things that work within your horse’s rhythm – as well as give him a rhythm to work to!