SHELBYGT NSM

First off i have a 1988 Toyota Corolla.
5 speed, 4 cylinder. For the last couple of months this car has been acting up, first it would miss and sputter then go away, then it would get worser, so i crawled under it looking for a fuel filter and no luck on finding it, note, this car is a very low riding car. So it's kinda hard getting underneath it. But when the car was over a half a tank of fuel it would run fine but if it went lower than a half it would start running rough, not wanting to accelarate, so when i push the clutch in and give it gas it sounded like only 3 cylinders was firing, and here lately it wants to die, shut off. I thought maybe a battery issue, so i swapped my jeep battery and put it in the car and no difference. There is nobody that i know that ever owned a later model corolla so i am stumped. So does this car have a fuel filter? And if it does where is it? What else could it be? Note that now it doesn't matter how much gas is in it. It will still run rough. So any information would be a great help.