When he moves the detour sign, and gets back in the car, Luke closes the door on the General but they are supposed to be welded shut.
When Rosco first sets the detour sign in the road to trick Uncle Jesse, the arrow on the sign is pointing to the left. A few minutes later, when Luke grabs the sign and sets it in a new spot, the arrow is suddenly pointing to the right.
When Cooter raises the hood of the car he gives Uncle Jesse, you can barely see the top of an air filter that would normally sit on top of a carburetor. But the close-up of the engine shows it has a supercharger with a butterfly valve intake on top.
When Sheriff "Spike" Loomis rips the trunk lid off of a car he pulled over, you can see the hole that was cut into it so it can be picked up and thrown. You can also barely make out the fake panels in the door and fender so the spike he uses can puncture the panels with ease.
When Sheriff Loomis is waiting at the roadblock for Jesse and Boss, the studio lights can be seen reflected in his sunglasses.