Sounds like there are several things that could contribute to the problem. First things first. Check the parts you have to make sure they are correct for the application. 2nd, check how many turns out the rear shock is. 3rd, what is your rear ride height? 4th. How many turns (roughly) did you have on the rear shock spring locking nut to achieve the ride height? If you having alot of turns on it to achieve your desired ride height, then the spring is too soft and you have too much preload on the spring. If so, when you hit bumps, it would feel very stiff and react very quickly and strongly.