When does the light come on? Will be important to know how long you drive it before it comes on, average speeds, in town stop and go or freeway, climbing hills or flat, etc. The light means tranny is generating too much heat. It is not good for the tranny if you keep driving with the light on (assuming the indication is not false). If you are on the freeway, make sure you are in OD otherwise the TC will never lockup and this in itself will cause overheating. Take it out on the freeway and watch the tach and listen and try to determine if it's shifting into all 4 gears plus the lockup shift. You should easily feel 1-2 shift, 2-3 shift, and then 3-4 shift once you get to about 45+ to 50mph, after that the lockup shift will be harder to detect but you should notice about a 200 rpm drop around 55+ mph on the tach.
Flush, filter and fill is also a good idea like others have said.
There's been lots of discussion on this tranny. The 3fe board is a good place to ask questions or search archives.
