polkatronron, it is confusing, even for those that live here. It could well depend on which state you are traveling in. Many states no longer have separate speed limits for trucks. I was traveling through Tenn. a couple of years ago, and wondered how my truck and trailer was classified, and even called the state police to verify......my unit was considered a car.
I don't think there is a cut and dry answer for every state.
Chap , DW Joy, and Fur Baby Sango
2006 Ford F150 Super Cab 4x4
2008 Surveyor 263