A few thoughts:
1. Are you sure you put "Shock" oil in your shock, or did you use fork oil? The reason I ask is that fork oil will not work in shocks because it will not stand up to the heat generated by a shock.
2. Are you sure you got all of the air out of the shock? When changing shock oil, air is the enemy.
3. You might have too little rebound causing a problem called "packing". Packing is caused when your shock does not rebound completely. Ironically, if you are experiencing packing, it will seem as though you have too much rebound. To test this, turn your rebound clickers out instead of in and go for a ride. You can experience the same type of problem if your compression is set too hard, so check this as well.
4. You indicate that your race sag is 4 inches, but do not provide your static sag number. This will help determine if your spring is correct for your weight. If not, it can feel as though you need to slow your rebound.
5. Shock seals do not go bad very often, so I doubt you need to replace this item.
6. I believe 3 wt. oil is way to light for a shock. I recommend you change to 10 wt BelRay suspension fluid. If you have the right spring and no internal shock problems, you might find that the heavy weight oil does the trick.
Rick