Difficult to tell without seeing the bass, but is the action now
too high? I had an Ibanez Musician bass (like the one Sting used but fretted)which was really nice, but I leant it to a friend who was going on tour - he put really heavy guage strings on and when he came back the bass had a huge bow caused by the strain - lots of relief!
I found that for me the bass was almost unplayable and it was physically very difficult to hold down the strings between the 3rd to 15th frets, so my left hand would slip and cause noises and buzzing as it lifted off slightly. I had to tighten the truss rod a lot to get it back to where I could play it without this sort of problem.
This was a good lesson for me in setup - I tried to do it gradually and nothing much was happening, so I thought I would sell the bass - by the time I had agreed to sell it was actually playing quite well - it had taken a few days for my changes to take effect! I regretted selling it ever since.
