It's not possible you would see a difference between P3D V3 and V4, because this seems to be a problem with the GSX .INI file we supplied with KIAH in the scenery folder, some parkings seems to be incorrectly flagged as "Right" preference only.
You can fix this in two ways:
- Opening the GSX parking customization page, select all parkings where you want to have a Left+Right pushback preference and choose "Both", then Apply the changes.
OR
- Run the FSDT Live Update now, which will download a fixed .INI file for KIAH