I had the same back pain problem on my America and bought a Sprint also last year (it was a 98). The good news is the back pain went away but the bad news is that it was killer on my hands and wrists. Ended up selling the Sprint.
I test rode a new Sprint with the higher bars and they were better, but hands still started to hurt after about an hour. Haven't taken the tiger out long enough to comment but seems like it might work better. Insurance on a new Sprint is also WAY higher than the tiger or any of the twins.
What I have now is the best of both worlds - a regular Bonneville with genmar bar risers and rearset pegs. Seems strange but the rearsets keep the pressure off the back and the risers keep the pressure off the hands. Plus I get the lower insurance of a non-faired bike and the ease of maintence of the air cooled twin.
