You shouldn't just verify that the port is correct. It is a question of verifying that your code - with your declared constants - always does the correct thing.

That you can drive a stepper motor doesn't say anything about the function of your LCD program.

If you add enough delay between each access, then you can measure with the multimeter and write down each step on a paper. Either compare with the datasheet, or compare with simular measurement when you run the display on the original - working - port.