i had this same question, i didn't like the answer i got at the dmv but i can't find a better one.

according to the clerk, "truck" plates only go on trucks with gvwrs higher than 7500 lbs. my truck's gwvr is 8900 lbs and i was given standard issue plates. unless she screwed up, i suppose that means it's up to you as long as you are using the truck privately. trucks with "truck" plates also don't get property tax relief.