Tired of my Sigma 18-200 DC lens on 550

I shoot sports along with general photography and pictures of kids, family & friends. I pp in LR3.

I like having the range of 18-200, but I just don't seem to get any sharpness in my pictures.

Could I see a significant improvement in another lens with this range. Or would I be a lot better off going with something like EFS 15-85 + EFS 55-250?

I'd much prefer a lighter lens, but not at the cost of much image sacrifice. Price not so much of an issue.