Need some help. Just put in a remanufactured long block in my 98 stang and figured while I had the tranny out I would drain the fluid & replace the filter (all 12.5 qts). All seemed to go well but when I buttoned it all back up and went for a short test drive, the tranny shifted late and hard from 1st to 2nd and the O/D off light started flashing and the check engine
light came on. Back to the shop put the check engine tool and got codes P0720 P1900. Said the speed sensor was bad. I replace the speed sensor on the back drivers side of the tranny. Long, short, same problem.
When I went to my local Advanced Auto Parts and ask which fluid the 98 3.8 required, they said Mercon V., so thats what I used. Digging around in different places looking for possible causes of the flashing O/D light I check in my Haynes manual and the manual called for Dex/Merc fluid on 94-98 and Mercon V for 99 on.
Now the question after all that is, Is it an issue to use Mercon V on the 98 and if so , is it the likely cause of the flashing O/D light.
Looking forward to ya'lls insight