I have a 2015 F250 Super Duty with a crew cab and the rear vents are barely blowing any air in either the heat or AC setting. The front vents are okay. The truck was obtained from a TX dealer and was dusty inside so thinking that the evap coil needs a cleaning. Also looking at installing the 19811 filter to help. Just wondering if there is something else I need to look into for the rear air volume as well.