not shifting into overdrive

[JT1007]

98 explorer XLT had to replace my drivers side cv joint already... however now that im done with that for some reason it wont shift into overdrive. i never had this problem before. o/d light is blinking now and it just wont shift did i do something wrong?

 

[swetrid]

It is probably not related but anything is possible. Codes would be helpful to help diagnose the problem.