98 durango wont move

this suv has been kicking my ass for some time now.. at first i had a trans. overheating light come on i pulled over right away and found out that it wasnt upshifting correctly my wife was driving and said it was running about 4500 rpms going 70 ..oh shit.. welll any way i ran the codes and found that it needed a speed senser..easy fix.. so i changed the fluid and filter using atf 4 instead of 3.???? and it worked great for about 50 miles then suddenly now soon at it gets even sorta warm it acts as if is in neutral all the time untill its cold again them its fine wtf..

I pretty sure you should have used the Mopar fluid ATF+4