A pull to the left or right in any vehicle can be generated by many different things.

You have all ready checked the most comon problem "tire pressure"

Another comon cause opf this is called " radial pull " this is caused by the radial bly's or cords in the tire that are not running true offten this happens in new tires that were not manufactured correctly. To confirm this is the cause remember in which dirrection the the vehicle was pulling then swap sides with the front to tire ( RT front to LT front and LT front to RT front) if the pull goes away or now pulls in the oppisite direction you have located the problem. ( replace the bad tire )

The vehicle aslo may need an alignment or it could have some worn , bent or broken suspension components such as ( tie rod end , ball joints , control arm bushings , struts , shocks . I have seen wheel bearings also cause a vehicle to pull of course the wheel bearing & wheel fell off when the vehicle was lifed in the Air but thats another story.

The only way to know what you need is to do a very good inspection of the suspension check the alignment and go from there. replace the needed parts or it may just need an alignment. good luck - Mike