Pls Help is it the tranny ???

I have about lost my patience with this whole entire situation so i am coming to you all once again for help with yet another problem with my ford.
I own a 98 4 cyl Ford Contour which has about 130,000 miles on it. Just about a week ago when i went to put it into drive it did nothing but spin and very slightly rock.
So after a few tries i put it into 2 and sure enough she moved. I brought it to my mechanic ( who was sure to remind me that he doesn't know anything about the inner workings of a transmisson) who told me that he doesn't feel that its necessarily a tranny issue but possibly an electric problem as if you get the car up to about 45mph you can float it into drive and she will stay there (like normal) - you can even hear the engine change into the proper gears .. that is until you have to come to a complete stop then you have to float it once more.
I have called a few tranny places and have been told about vents and filters one even mentioned something about links (have no idea what that is) but they are all sure that i have to install a brand new one so before i go thru all of that i wanted to ask you all for your opinions.
thank you for any help that you can provide as it is greatly appreciated

when was the last time your transmission was flushed?