My flat speed is better than most other cyclists but come to a hill and the power I seemed to have on the flat just isn't there and cyclists I've overtaken catch up. Why is this? What can I do to improve other than try to lose weight and cycle more? I think my technique and bike fit is ok, I don't feel pain, just don't seem to have the strength. I consider myself to be a grinder rather than a spinner. Thanks to anyone who can help.