I loved this series as a kid for many reasons. First and foremost was it was about truckers and there was quite a bit of truth (balanced out with a healthy scoop of Hollywood bullshit) in the storylines compared to most trucking shows, films, ect. Second, I was a big fan of Claude Akins. The fact Merle Haggard did the theme song didn't hurt, either.
After the pilot they magically got a much nicer truck (first walk-in sleeper I ever saw), but with the same paint job.
Here's the pilot episode/film of Movin' On.
Series theme song: