Autonomous trucks are just some minor differences from Autonomous cars. No auto manufacture dares risk someone else come out with an autonomous car that is enough safer than human drivers that governments mandate it. This is mostly about all the patents needed to make it work that the first mover will get. As such all car companies are investing in this to ensure if someone makes it works they will have it too, or at least enough useful patents that they can get a good licensing deal.

I think Tesla is the only company attempting this alone, all the other car manufactures are just in some form of partnership with others. These partnerships are known to include the big truck manufactures. I suppose there are a few car companies not investing in this (either tiny, or not selling cars in western countries).