To know for sure if it's your GPU, have you experienced graphical glitches in other games, and even the desktop?
GPU issues could happen in a game, but not in others. Back in the days I was having serious GPU artifacts like that in GTA:VC, but not in other games. Then found out the GPU was about to leave. I'd first make sure it's not just a simple problem, like a mod or accidentally saving a 'broken' map over the original one. Go to Documents/BeamNG.Drive and delete everything (Backup your mods if you want, do not put them back). If the problem still persists, check your GPU drivers, and eventually clean install them (Not sure if the AMD installer has an option for that, you can use this eventually: http://www.guru3d.com/files-details/display-driver-uninstaller-download.html ) Last, it could be an actual hardware failure.