Take it to a shop. When the OD light flashes somethings wrong and it's probably overheating. I've got a 98 'Tour with a bad ATX (torque convertor) right now, and driving it just 60 more miles after the first signs burned the clutches out... more $$$ out of my wallet.
The ATX's in our cars are dogs and are prone to overheating. I'm installing a Level 10 rebuild kit and external tranny cooler next week. I reccommend the aftermarket cooler to everyone with an ATX.
BTW, how's the fluid look? If it's burnt (brown, strong smell) you're due for a rebuild. By that point it's too late. If it's still pink you may be able to pour in some Tranny Dr. or something and pull through. Sounds like your clutches, though... if you put
too much fluid in the tranny, it won't shift right. Same thing if it's very low.