When I was on my way home on the expressway going about 70 mph, the rpms suddenly jumped to over 6000 and the engine overheated. I pulled over and got the thing towed the rest of the way home. I noticed that when I drive and I go over 30 mph it starts to do the over-revving. its the original 5.7 liter and the 700R-4 transmission. Just wondering if I need to replace the 700-R4 or if something else it wrong with the car?