My sister has a 2004 GMC safari van. A few months ago, the van started having a very rough shift and excessive revving. We took it to a mechanic who found a transmission leak. They fixed the leak and recommended that we use Lucas oil transmission fluid to help with the rough shift. Since then things have gone from bad to worse. The van will not go over 45 mph. The engine excessively at 35 mph. After 35 mph, it appears something also goes wrong in the electrical system. At 35-40 mph, my dash goes from lit to dark. Also I have lost the use of my power locks and since this issue began, I have lost use of 2 of 3 of my cigarette lighters. What is happening here?.