Thank you for the additional information. As you maybe begining to discover there is much more involved in this than you might have expected. Forgive me of I sound abrut at times. If I do it is not intended. Intermittent faults are amoung the most challenging and rewarding problems that we face. In your replay you indicate that the engine can be free reved in park. This is as good as neutral. Disconecting the battery does nothing other than code your radio. The control units (ECM's) in your car have hard memory. When the fault occurs does the transmmission actualy shift into third gear then back to second? or does it never make it out of second. I read it that it does not make the shift.
Can the car be put into drive and while holding the brake what RPM can be achived while breifly appling full throttle?
You should see 1500-1800RPM and have a extemly high tourqe load on the brakes.
Benzmacs point on the crank angle sensor L5
is a valid possiblity. I have had a few (8-10) The primary thing that I have seen with this fault is the engine will seem as if the ignition timeing is incorrect. A DTC will be set if the sensor is faulty but it erases itself after it sees a valid signal and the engine has run normaly for a period of time.
How long I do not know. If this was the case the time that the car was at a dealer when fault was happening they should have gotten a code. Do not rule this componet out.
Another possiblity that you can look at yourself is the carpeting and floor mats around the gas pedal. Insect them for being bunched up under the pedal. While you are there look at the kickdown switch that is located directly under the pedal. (round and black) Push it down and listen for a click then release and listen for the click. If this is sticking down it could hold the transmission in gear and not allow a upshift.
It dosent sound like this is your problem but it is easy to check anyhow. Have the dealer perform a fuel pressure and VOLUME test. Volume being much more important than pressure. At the same time have them check the adjustment of all the throttle likages and set the lenghts to specification. As the transmission control pressure cable adjustment.
One last question When the fault is occuring and you attempt to drive does the engine buck choke or sputter? or does it just feel as if something is holding the car back ie as if the brakes were applied.
If you can think of anything else that might be helpfull please post. A complete history of a car is eveybit as important to the diagnostic process as it is to a Dr.