This is a common problem with Chrysler corp transmissions. This
is called "limp mode". It was designed to help you get home in the
event of trouble. The transmission comunicates with the
transmission, When it sense's a problem it goes into limp mode. The
only thing to do is take it to a transmission shop and pay for the
diagnosis. 90 percent of the time the transmission needs to be
rebuilt of replaced from about 75000 miles and up.
You may just need to have the fluid and filter changed. Do you
have a lot of miles on the car? That's the first thing I would do.
It's also the cheapest route to go.
I can't recall where I read this at originally (it was online
but it was a reliable source, that much I recall at least) but the
problem may be a defective aluminum seal in the transmission. It
lets in moisture. To repair you will need to completely drain and
dry the transmission then fill it up with tranny fluid. It's not
good enough to simply drain the transmission. You must open it up
and let it fully dry. To stop this problem from recurring replace
the alumiinum seal with a steel one (they are less likely to warp
in hot and cold conditions). Any reliable auto repair shot that
specializes in transmissions should know of this problem and how to
fix it. Just ask them about a bad seal in ultradrive transmissions
and if they can drain, dry and replace the seal. See below for more
info (nothing on the moisture part specifically though, sorry).
http://www.autosafety.org/article.php?scid=100&did=563
http://en.wikipedia.org/wiki/Chrysler_42LE_transmission
