I have got the exact same problem, last year i did some demos for my local bike shop, and they filmed it all to play in the shop (theyre still playing it now which im quite proud of :D ) When i watch myself on the video, i dont seem to be putting much effort in at all. When i watch realy good riders they are really explosive and can up well high, but i cant back wheel as high as i know i could because my confidence stops me putting my maximum effort in. its quite annoying.