All companies are different. Our trucks are governed, but they don't look at your average speed or anything else for that matter. They just don't allow our log books to show over 68 MPH. Some companies actually track how fast the truck was truly going, and the top speed the truck has reached.
As for the software though, I don't know of anything that can be used for this other than the actual tools that a tech would have that hooks into the computer, which is very expensive. There are people out there that have these things and will do this for you (for a fee of course).
I don't think there is any simple software that you can get though for this. I might be mistaken though