1995 century transmission

I have a 1995 buick century that will not shift out of 1st gear till it is driven 3.0 or 4.0 miles and warms up .Once it shifts it will work fine,Ive change the fluid and filter with no help.It has a 4T60E trans which is the 4speed auto with overdrive.Ive been told that the 4T60E to replace it came out in 94 and 95 buick century and olds. Does any one know if they make a 95 century with a 3.1 with out the overdrive trans

I can only think of one repair you can do at home that may help:

Check for a sticking spool valve. Should be able to remove it with a magnet inside the hole where the modulator valve goes. Perhaps someone else knows more.