96 explorer wont shift into 3rd or 4th

[mritz]

I hope I am not asking a question that has been ask before,I have searched the forum for several days and have not really found an answer
1996 Explorer EB 5.0L V8 2wd 200k from what I have read this is a 4r70w
recently bought this with know shift issue but price was right
Originaly would not shift from 2nd to 3rd or 4th also had severe shudder from dead stop once trany warmed up
I did a complete fluid change including T/C drain and new filter refiled and added 1q of lucas trans conditioner with refill
the old fluid was black but did not smell burnt,not alot in the pan magnet had some debrie on it probaly the thickness of the magnet
Now shudder is GONE I can get it to shift into third if I accelerate and let off gas but it is like it shiffted into neutral 2nd will drop back in around 20mph and will shift at high acceleration into 3rd? around 45
Am I looking at another trans or is there something else that could be the problem?
If I am looking at another trans my next question I found a 98 Mountinere with a 4r70w and only 100k on it,is this a direct bolt in or will I need to rewire the computer harness?
Thanks for reading and any help you can give

 

[mritz]

 

[mr2fix2it]

http://www.car-part.com/cgi-bin/search.cgi hope this helps looks like only 96 97 fit

 

[mr2fix2it]

http://www.car-part.com/ I see other link wont work try this but you need to enter info.