i bought this car used and i'm not sure how they  often they changed
the transmission fluid or what kind is in there.  when i bought it i
drove it for about 200 miles and the engine light came on , so they
must have reset the battery or something to get the engine light to go
off, before i bought it.

How much of the work can or do you want to do on this?

If this was my vehicle (keep in mind here I have a scantool that
will read transmission codes) I would do the following:

"Ultradrive (41TE) transmission fluid flush" located here:

http://www.allpar.com/eek/atf.html

although I would use ATF+4 in your model.

also, read the following:

http://www.allpar.com/fix/trans.html

I would ALSO pull all electrical connections to the transmission
one at a time and give them a good spraying and scrubbing with
contact cleaner (available at an electronics distributor) immediately
followed by a good soakdown of WD-40 which will drive out any
water and remaining contact cleaner.  Don't forget the grounds as well
as the connection on the transmission computer itself.

With a big slice of luck, you may possibly see the problem disappear
a week or so after flushing.  If it does not, well you can get a rebuilt
selonoid pack for about $120.  If that doesen't fix it, it's then teardown
time - you got something jammed up inside the transmission.

Note that you can take it to a place that will hook up a pump
to the transmission lines and "pressure flush" the transmission.
It will do the same thing as above, just faster.

Ted