2010 Ram 2500. Noticed the steering was getting a bit....chunky. Like chunks of dirt going through a hose feeling on the steering wheel. Thought it might be the steering stabilizer on the front solid axle going bad. Checked the fluid level and it was fine and clear looking. A week later I checked it again and the cap to the fluid res. was gone. I know I tightened it. Could it have blown off from pressure? Could the pump be bad? It has a steering box that was replaced due to leaking a few yrs ago. Any thoughts?