My daughter asked me about this word today — asking if it was named after a bully that sleeps a lot. I had to say I didn’t have an answer for her, so I had to go to the books.
Turns out, the word comes from late-19th century, long before the construction vehicle. It originally was “bull-dose” and meant to whip and beat in order to get to do something. The earliest sentences made references to people who had bulldosed their slaves before the war or bulldosed their workers. My first thought was that it came of the dose of a beating necessary to get a bull to comply, but Word Wild Words found a great line from the Gettysburg Compiler in 1877:
“In very obstinate cases the brethren were in the habit of administering a “bull’s dose” of several hundred lashes on the bare back.”
The reference here seems to suggest a dose of a bullwhip. There you have it.