Any white smoke coming from the exhaust? This could indicate a head gasket leak. Have you pulled the plugs to take a look at them? If they're extremely clean, or if you notice coolant on them, again, could be a head gasket. Take a look at the timing cover area, especially if your 97 is a 4.2L.
Post your engine and mileage. I think we could all help you much easier if you do that. Good luck!