34 psi is not high. i run 38 psi on my 17". 32~36 psi should be good for a 15". never run anything below 32 psi,that's as low as i'd go. best thing u could do is replace the shock and spring mounts. these are rubber and tend to wear out ~50k...i suspect that's what ur feeling. (s80 models have shown premature shock/spring mount wear at 20~30k.) also, some shocks may wear faster, so u're not getting the damping u need...not likely at 50k tho, more like 80~100k...i'd go with the mounts first