This article is from the Toyota Tundra FAQ, by Steve Yee with numerous contributions by others.
Well, it depends on how you count things. There are actually 9 crossmembers.
There is one set of crossmembers that are formed in the shape of an "X". In
the Model Year 2000 literature, this "X" shaped grouping was considered one
crossmember. Now it is considered 2.