I have to laugh. Anyone that buys nitrogen charged shocks of any type should have a resource for measuring pressure and setting or restoring said pressure. Letting out the pressure with little spurts until the truck no longer pulls left is goofy. You should have bought a standard stabilizer if this is your approach. I have found that 125 psi with Thuren stabilizer negates most road crowns and is not much of a pulling issue on level or left crown situations. I have stock tires. I live a hundred miles from nowhere so I bought a nitrogen tank form a welding supply outfit, had a high pressure hose made up at a hose supply place with a pressure gauge in line with it, and got a special fitting from a race outfit that allows you to release the pressure from the supply hose and disconnect from the shock without changing the pressure in the shock from where it was set. I understand that buying your own nitrogen charging stuff is expensive and cost prohibitive. Just remember, it can also cost you money to get it done (especially correctly). I also believe that like a tire (although slower), a shock can lose pressure over time.
Motorcycle dealers sometimes have the nitrogen charging equipment in there service departments.