Early in the film when Johnny gives Burke a ride downtown he parks directly behind a 1958 Chevrolet. In the next shot with Burke now out of Johnny's car, the parked car in front is now a 1959 Chevrolet.
As Slater drives to Melton, long shots show his car to be a somewhat dark color. In close shots, the car is much lighter.
As Slater first drives the souped-up Chevy wagon, he grinds the gears. Later, as the speedometer climbs to 100 mph, the left side of the Powerglide shift quadrant is seen on the steering column. Automatic transmissions don't make gear-grinding noises.
Slater and Burke, in car en route to case the place which they plan to rob, are seen going southbound on NYC's Harlem River Drive towards Manhattan. In next scene, Burke says to Slater, "... it's about 100 miles up the Hudson..." They are going in the wrong direction for upstate NY.