Soft shifting? You should check your shifter cable. My cable was fraying inside the shifter body, near the end of the cable. It was only a couple of years old. Finally, on a ride, it wouldn't shift to the largest cogs, and a mile later, broke off. (It's hard to get that short broken end out of the shifter, too!)
I think that you have to get a whole new shifter mechanism, no separate parts are available. But the shifter is supposed to last longer, and not need G spring replacements like the old version.