Engine, Slip, and TCS Off lights are on?

It started with my engine light staying on. Now the Slip and TCS Off lights are staying on. Sometimes it is hard to start. It just turns over and over. If it does start right away, about 1/2 a mile down the road, the car shuts down. When it finally starts, the lights are on again. Also, My gas mileage has dropped like 30-40%. I could get about 340 miles per take and now its like 200. I have an 04 Nissan Quest. Have you ever experienced this or know what it might be?