95 lumina transmission od issues I think

To anyone who can help!!! I have a 95 lumina with 211,000 miles original transmission (2nd issues due to head gasket) and within the last three weeks the od seems to have gone out of the car and it runs at about 3500 rms. If I let the car sit for a few hours and get back in it is fine. Well all of the suddent the check engine light came on as it did this tonight. I probably need to change the fluid and filter but wasnt' sure if this is a common problem. Any help would be appreciated, I want to drive this thing forever!

Thanks
Andy

Get the error code read.

What does the trans fluid look like? Is it still reddish in color, or brown and acrid smelling? You should get the code pulled as the previous poster suggested before going too far, but a trans filter change wouldn't hurt anything. Don't get a fluid exchange, it's a very bad idea in a high mileage car. Just drop the pan, change the filter, and replace only the fluid that you drain to drop the pan.