When the G.T.O. pulls into the gas station it's extremely shiny and clean for having just driven through 3 states.
The cost/gallons numbers on the gas pumps change several times during the gas station race set-up scene.
At the garage where the race is being set up, watch the crank of the hand mangle as it mysteriously changes its position throughout the clips.
In one major scene the Mechanic (Wilson) scopes a drive in parking lot for a competitor. He notes "a '32 Ford Coupe with a 427 and 11" rubber". The car is in fact a '30-'31 Model A Ford with a GM radiator grille. The rubber and Chevy engine appear to be correct, though.
The interior of the GTO changes between chocolate brown and black.
Claimed that the 'Cuda they raced was a Hemi with a Torqueflight when in fact it is an AAR 'Cuda with a 340 6pack.
The wheels on the GTO change from GM factory rally wheels to Keystone mags.