Are you able to use the Radar Trailer or the White Western/DAN? Because I did the same (after my old savegame wasnt loading at all), even did the mission to get the radar trailer - and I do have NONE of these mission trucks. Neither DAN nor White Western nor the "officially unlocked" radar trailer. I am not sure if this is a game bug. And I even tried to remove the "lock by mission" from the XML Files of the truck. No way, I simply do not have the e.g. White Western / dan or exploration unit available.