Hey guys. Im really having suspension/ vibration problems with the 404st. im pretty sure it has the AG-400 Air Glide Suspension. Just wondering does anyone know the correct height for the Height Control Valves?? Yesty only had a light load with 22 sp's (got a 24 pallet 48-ft) the left hand side gauge was readin jus over 3 1/4 and the right hand side was jus under the 3, it was riding real good on the smooth stuff and a few bumps here and there but the vibration jus wont go away!!!...we adjusted the sleeper cab lower but it didnt help!. does the 60 pound check valve stuff up every yr and would a dud HCV be a prob to?