They've always been nice to me, but I'm smart enough to know that starting off an inspection with an attitude is a battle the trucker will lose every time. So far, I've never had an issue with a DOT officer from any state being less than professional, and they're a wealth of knowledge and interesting facts if you can catch one in a talkative mood LOL.
It's probably a great job, assuming you have a thick enough skin to handle it when a trucker (or anyone else for that matter) decides to get an attitude the moment you stop him. And some of them will test your patience for sure. We have more than our fair share of jerks in this industry. Also remember that there are risks to the job too - you'd still be a police officer with a firearm and subject to the nutcases out there. And there's the risk of conducting traffic stops on the side of 70+ mph highways.
Personally, I think it would be a cool job, but my psychological profile indicates that those who committed crimes and ran from me and forced me to chase them would receive a beat down from me when I caught them that would be considered... inappropriate by most department standards. So that's why I'm a truck driver and not a cop. LOL.