Are you turbo'd or N/A ? With 3:55 rear end your gonna need to downshift manualy to keep the RPM's up on a grade. I haul 9K of trailer and I normaly have to cancel O/D long before I get into the hill and I have 4:10 rear end.
Try keeping the RPM's up at about 2800-3200 when your going up the hill. I will come off the "go" pedal just long enough to take the strain out of the drivetrain and then move the shifter. E4OD and 3:55 gears are great for the flat road.
As for the O/D light flashing: The Tranny computer has detected a problem and you need to retrieve the code(s). You need a FORD OBD I code reader or an analog OHM meter and this link:
Don't give up your diesel rig..I had a gasser (460) that drank fuel @ 7.5 MPG with the trailer.
Thanks for the response. Just out of curiosity, why do I need to downshift for the hills? My f150 had the same transmission (pretty sure about that - 1997 F150), and I never downshifted that thing going up hills. The biggest hills I go up, it may have dropped to ~ 50ish, but never down to 40. Is it just because of the torque of the diesel motor?
Will the OBD1 reader read all of the transmission codes as well as check engine light codes? Or should I do the transmission codes just with the analog/ohm meter?
Any chance the tranny issue killed my gas mileage?