If you use the two external interrupt pins to capture the pulses from the hall sensors then you won't miss anything. Just make sure that the code in the ISRs is a short as possible - perhaps something like
void wheelPulseISR() {
wheelPulseCount ++;
newWheelPulse = true;
}
void fuelPulseISR() {
fuelPulseCount ++;
newFuelPulse = true;
}
then your code in loop() can check for the new pulses and read the pulse count
...R