My own opinion here, is that dreadlocks say "look, I don't wash my hair very often at all! Wanna touch my filthy head?"
Our dispatcher (one of them) always likes the guys dressed ready to work. It can be nice clothes, but jeans, boots, shirt, etc. The guys that wear suits or slacks he is not impressed with as much. One time an interview showed up with his gloves in his back pocket and He wanted to hire the guy on the spot!! Each guy doing the hiring probably has a different opinion though.
The rule of thumb I've always used for interviews, with any company, are dress one step above what is expected of you at work. Since you can pretty much wear what you want in the trucking industry, I agree with the others. Nice clothes, khakis polo shirt and well groomed. I'm a girl (obviously) so I never overdo perfume, makeup or jewery. Also I always kep my visible tattoos covered until I know the company policy on tattoos. Wishing you the best of luck in your interviews!