my dog pants uncontrollably in car

My 8 year old dog Rambo was 6 1/2yrs old when we got him. He was orphaned by his only single owner who passed away. My concern is though going in the car was new to him, he has learned to love it and gets extremely excited when the "car" is mentioned. But once in the car he pants Extremely Hard, and non-stop, which scares me into thinking he could pass out or injure himself. I am also concerned that he may think he is going "home" to his original owner after all this time. Is that possible? or has he forgotten that time period. Is there anything I can do besides discontinuing his rides to get him to calm down and enjoy it?

He's likely hyperventilating out of sheer dizzying happiness at going for a ride. (You did know that there's a car-shaped gene in all dogs' DNA, didn't you?) Dogs pant when they're very excited.
   
After a year & a half, I don't think he expects to go to his previous owner any more. Does Rambo show every sign of loving you very much & being very happy to see you when you come home (even if you've only been out of the house for 20 minutes)? If so, then he's transferred his affections to you.
   
Try some of the natural dog tranquilizers that are sold at the pet store, & dose him as per instructions before a car ride. See if that helps.