T in a small line from the back side of the LH steer cylinder to the front if it. Essentially bypassing it to allow air trapped between the two front cylinders to be pushed through. The only way the system can purge with out doing this is back through the RH steer cylinders built in purge valve which can be difficult sometimes.
You can also check the LH steer cylinder for bypassing by first setting the front wheels to 90 degrees in side mode. Shut the truck off. Cap and plug the front line on the RH steer cylinder. Mark tge chrome rod of both front cylinders. Turn the truck back on in LH side mode. Turn the steering wheel 2 full rotations clockwise. Then 2 rotations counter clockwise. Now check the marks made on the chrome rods. If either cylinder extends while the the line is plugged will be the one bypassing internally.