When you are rebuilding the shock, make sure you cycle the shaft and listen for air. It does take some time to get the air out of the shock valves and shaft. I always pre charge my shocks with compressed air up to 150psi and cycle the shock again when it is fully put together to check for leaks and that the shaft will bottom out. Then drain the air and recharge with nitrogen.
Shock oil is rated by the viscosity index is what sets the heat it can take. Everyone has their own shock oil and viscosity rating. So a 10wt in Fox is different then a 10wt from WER shocks oil.
Shock PSI is what helps keep pressure on the oil so the shock valving doesn't cause cavitation which is air in the oil. The more air, stiffer the short choppy bumps will be. But the more air, the harder hits (jumps) it will be able to take without cavitation and fade.
Also, when you are taking your shocks apart. You need to inspec the shafts very well.