The vent that Luke looks through is at the very front of the trailer, which means it would be taking the full force of wind as the truck is moving. But when he opens the vent to see inside, no wind is blowing anywhere inside the trailer.
When Daisy throws her purse into the General Lee, the front left fender is bent back in the view down the car. When the Luke drops Dewey Stovall off across the county line, the fender is in perfect shape.
When Bo Duke passes the purse with the gambling winnings to Luke Duke in the General Lee, there is a large dent in the front left fender. In the next scene when Dewey Stovall exits the General Lee, the dent is gone.
When Luke Duke drives the truck in reverse, the tire marks are already on the road, indicating that the film was simply reversed.
The semi is referred to as an 18-wheeler, but the tractor clearly only has one axle and four wheels in the back, making it just a 14-wheeler.