I am looking for ideas on a vibration/rattle that happens on my 2003 2500 Chevy HD (236,000 miles) at about 30-40 mph and higher but not as pronounced in the left front area near the wheel well/fire wall. The noise/feel happens on rough roads with an inside or outside corner including both up and down hills. The feel happens worse with a loaded (wood/camper) truck but also happens empty. Braking does not seem to have any affect on the issue. I have changed out all the steering joints, intermediate steering linkage, brake pedal bushing and brakes. I am looking to see if anyone has ideas on what to look for. I have not changed control arm bushings. Any thoughts? Thanks.