The A0 and A1 aliases are for when you want to use analog pins as digital pins. That's what this part looks like you want to do.
int voltin0 = analogRead(A0);
int voltin1 = analogRead(A1);
But, this part of the code looks like you want to use the analog pins as analog pins. In which case none of that crap in setup() belongs there, since analog pins are, by definition, INPUT, and you do not want to be turning on the pullup resistors. Also, you want to use 0 and 1, not A0 and A1, to make it clear you know what you are doing.
Serial.println(voltin0 - voltin1);
So, every 5 milliseconds, you want to write potentially the same value, as a string, to the serial port.
I'd think that it would make more sense to only write when the value changes.
If what is connected to the two analog pins is from the two sides of the motor, the voltage at those pins will be the same, so you will be writing a continuous stream of 0 to the serial port.
I can't see that being useful. Even if you measured accurately the voltage or current applied to the motor, how would that information be useful? What, exactly, is that motor doing?
a linear webpage scroller.
What, exactly, is a "linear webpage scroller"?