Another thing to check is that there are equal number of links in each track, no unknown to be different, if they are worn.
Failing that, and track tension, band adjustment, etc., are correct, then it may be "track drift". This can only be checked on a flat smooth surface, a long time since I did one last, but it checks how far offline the vehicle goes in 100 feet ( I think, but might be less). This is corrected by shimming behind the appropriate sprocket. Obviously more noticeable when driving on straight roads, more than cross country with no clear track to follow.