A odd surging issue

[410explorer]

So after all the recent work my truck is running better then ever but just developed a new issue if im on the highway and let off the gas like to take a exit the rpms will surge up and down about 500 rpms then level out as i continue to slow down it does not do it at idle any ideas where to look

 

[EB4X]

Has it ever done it while accelerating too ? Mine routinely did surging when accelerating from the 20 to 40 MPH range and it turned it to be ONE bad o2 sensor.....NO CODE ! ! .... The way I figured it out was to unplug one at a time and do test drive until symptoms disappeared targeting bad one.......your PCM will use default presets when it can no longer read connection to each sensor....and will run DECENTLY like that....