Get a fixed, or build up your own, and practise on smaller hills, relax, then you will eventully develop a smoother action and the 'bumping' will be eliminated. I rode for years with a 24 speed then built my own fixed - shotblasted a John Perks frame, painted it, assembled my own wheels and everything else as well. Learnt a lot that way. Now building one for the track and a 'fun' fixie. My style on the 24 speed is more relaxed and thoughtful as I am more able to control my pace and effort.