Ford 2006 super duty E 350 passenger van / after sifting out of second gear it just revs the engine. If I switch it out of overdrive it is drivable but at higher RPMs

Ford recommends draining transmission, cleaning the pan, and changing the filter every 30,000 miles. Here's how to easily do that:

https://www.askmehelpdesk.com/cars-t...ml#post1873132

My recommendation is to use Mobil 1 Multi-Vehicle Synthetic AFT or Amsoil Universal Synthetic ATF.