Is this a MIA Jazz or P bass? I don't see that you said. Could be if it's a P bass the neck has become a bit fat for your with the RSI. I have tendinitis and I find that a thinner neck and round core strings (DR Hi-Beams) has helped me a LOT. The other thing is that Fenders have a rounder radius neck, which is to is a little harder to fret than a flatter radius.