Then, yes, look at routing from filter to side of coach.
Many chassis are shipped with a long flexible hose so that the coach maker can locate the intake where they want to.
Often, this hose is WAY too long for the run and just shortening the hose reduces restriction.
Also, be aware that if the filter element has gotten wet, that really restricts air flow, so verify that your water drain is functioning/is open.
Has the air filter minder reading always been high, AND, did you reset it after installing the new filter?
You would need to post pictures of intake and hose routing for us to really comment.
