I've had a puppy for a few months now...a failed foster. He spent the first few months of his life in a crate with no socialization. His first ever car ride was when some stranger grabbed him, wrestle...
Introduce very short trips in the car, just a couple minutes at first then stop and do something he likes like playing ball, petting, tug of war, etc for awhile. Load up and go home and repeat the fun.. If it looks like its working gradually expand the radius/ time and then include multiple stops. Not sure if its anxiety or motion induced at this point. He will associate fun with the vehicle, has worked for me in the past. Something to try.