I have a 95 tracker that is doing almost the same thing. It runs ok until it gets hot and then the white smoke starts it runs rough and it also leaks fuel out of the cat. Convertor. I changed wires, cap, engine temp sensor, ecm, coil. At my wits end. I don't think its a head gasket issue cause it doesn't smoke for the first 20 or so minutes. Have you fixed your problem yet and does my problem sound like what you have going on with yours?