Shifting issue 3.8L V-6
I have a 1999 Pony with 138,00 miles to it. I have been using platinum spark plugs new wires, all fluids are topped off, transmission fluid looks nice and clean on the dipstick.
Now I have tried to disconnect the battery for the night twice so far. The first time it started shifting like new, until a week later. Now I disconnected the battery again yesterday and it was unplugged for about 18hrs. I put the cable back on and started the car and let it idle for a few minutes taking it down the street and it started shifting at about eighteen mph instead of eight or so. And this is from first to second. I can start driving with the automatic selected in it's second gear instead of the overdrive gear so once I get it up to twenty five miles per hour I just let off the gas and bump it into the overdrive gear and it's normal.
I can get the fluid and filter changed for about fifty dollars by a friend at the ford dealer. What do you guys think I should do? I'm really starting to think it's the main computer instead of everything else on it. I'm a gentle driver as I have a '76 Bonneville brougham that is a nice big body so I like to drive my cars easy because of that one.