When I do my shocks I want a very slow re-bound of at least 1/2-3/4 of an inch.
My shocks are like butter..
I also would reccomend using Green slime when you build them.
Put it all around the o-rings and then (before you put the piston in) take a Q-tip and stick it inside the shock. What you want to do is cover the inside of the hole.
Then take the green slime stick it into the bottom of the chock (where the piston would go) and squeeze squeeze squeeze. It will take up and air pockets in the O-rings.
I didnt change my shock fluid for 2 gallons.
When I pulled them apart I had not one speck of dirt in three of my shocks.
The other was very minnimal.
Also, make sure you use shock boots.