Well, when the temperature drops, your car uses more gas! In the winter time the gas mileages DO lower than during summer time. So expect that to happen. When the weather is warming up You'd see improvement with mileage.
BTW, if fuel DO leaks you'd know for sure because the "Service soon" lights will come on immediately when computer sense loss of fuel pressure, or leak. Only 1996 or later model have this feature. (VERY Limited 1994-1995 models have that too)
