I'm looking for some help dealing with a 1999 Taurus LX Flex Fuel.
In slow/bumper to bumper traffic, or at any slow cruise, such as looking for a parking spot, the transmission jerks between gears, as if it is looking for the gear it needs to be in. Seems to be shifting between 1st and 2nd gear. It's almost like something is telling it what to do, and it's just following orders. Also seems to do it more when the car is warmed up
If I shift it into low, it's as smooth as silk, and runs fine.
It runs great down the highway, and the engine purrs like a kitten.
I really like the car, but can't seem to figure out why it does this. Check Engine Light is not on, and as I said, it just flies down the highway. All other systems operate great.
Anyone heard of anything like this? I've seen other posts about it, but no suggestions.
Any info would be helpful. I have done a tranny service, and did use Mercon 5.

I have a 2000 Taurus SE, with the Duratec engine and AX4N transmission. It's an incredible car. However, when I first serviced the transmission at 29,000 miles, I was very surprised with all of the crud in the bottom of the transmission pan. In my opinion, it's a good transmission but requires the owner to follow a very good preventive maintenance program. This is the consensus opinion of members of the Taurus Car Club of America.

Accordingly, I drilled a 1/2" hole in the pan and installed a B&M transmission drain plug. It turned out that Ford had embossed a raised "O", where I decided the plug should be located. This allows me to easily drop and clean the pan, change the filter, and refill the transmission with Mercon V every 30,000 miles. As you know, the pan gasket is reuseable and represents, to me, a stroke of brilliance on behalf of Ford. These Gen IV transmissions demand cleanliness, in order to up/downshift properly. I would only use Amsoil Synthetic Universal ATF or Mobil 1 Synthetic Multi-Vehicle ATF in them. These electro-mechanical transmissions are unbelievably complex, eclipsing engines in terms of complexity, and require the cleanliness afforded by synthetics.

If you have been running the standard Mercon V ATF, I would either switch to synthetics now or run an AutoRX program to clean the varnish/sludge that may be developing on the servos and internal valves. Improper shifts are usually caused by varnish and sludge. After switching to synthetics, disconnect the negative battery terminal overnight, in order to force the transmission to relearn proper shift points. You may want to try this now and see if it helps. I take this a step further and even drain the fluid in the torque converter. This allows me to change 13.4 qts. Of ATF, rather than just 7 qts. Some people I know do all of this on their Taurus/Sables, plus install an inline ATF filter; e.g. Magnifine, which they change annually. My Taurus gets driven hard, all over Texas, in 100 degree heat--hauling 3 passengers with luggage in heavy traffic. Still, it shifts flawlessly. Hope this helps.