For your weight, I'm guessing that your shock should be closer to 90 psi; you should check the manual for the exact pressure. As for sag, you should be looking at 20-30% sag, not the 70-80% you have now - otherwise you are wasting travel, and you must be bottoming out that shock like crazy! You can get a shock pump for $20, and it's worth it, especially in yor case.