Be patient with it... mine has been overheating only when ~2 hours into the mail route. Today when it happened I tried burping it and it kept the temperature down, but then I noticed that my heater only blew hot when accelerating. Eventually it overheated again, and so I burped it again. Same thing. Third time, I removed the plug too soon and coolant spit in my face
Fourth time, I took my time, opened everything, ran it until it started spitting up, let it cool, did it again, then filled VERY slowly until the bleeder holes and under the cap were full and had no obvious air bubbles coming out. Sealed everything up, and it got me through the rest of the route.
BUT, I'm still not confident that I did it right so tomorrow I have the day off and will do a "dry run" to see if I can get it to overheat again. I never want to see antifreeze again in my life