How can I improve petite allegro/ grand allegro?

I have been dancing ballet for 14 years and I must say that I have worked hard and become a strong dancer. However, when it comes to petite allegro and grand allegro, my instructors tell me I need to improve. I have a really hard time with allegro on the whole, but specifically I feel like my bottom half of my body is detached from my top half and I can't seem to get my feet to move fast enough or my legs to use pleay enough (bad spelling, sorry!) Also, my leaps are not where they should be as they are low and uncoordinated. My turns, adagio, and barre are by far my strengths but I would really appreciate help with my petite and grand allegro so how can I improve? Any advice is appreciated!