When Jim leaves Rocky's house...the bad guys (Dennis Burkley and accomplice) car (what appears to be Kojak's cruiser) is not visible, though the bad guys are waiting inside. When the bad guys leave, their car is now visible, though neither one went outside to move it.
When Jim and Rocky are trespassing...Willie's gun is in his right hand. When they pan in for a close up...for his response to Rocky's question about out of season hunting....Willie's gun is in his left hand.
When they pull out for the departing shot...the gun is back in his right hand.
At one point when Jim and Rocky are being chased in the stolen truck through the orchard, when the truck they are driving is shown, it is creating a huge dust cloud. But when the Ford Gran Torino that is chasing them is shown, it's relatively clear in front of that vehicle and the Ford is also leaving a dust cloud. The Ford is supposed to be right behind them in the story, in fact a man in the pursuing vehicle is shooting at the truck.
When Jim and Rocky leave the restaurant, Rocky's tie length is changed. While it's possible that Rocky retied his tie before they left, it's not likely. Also, note the bandage on Rocky's head is moved.
While Mr. Rockford and his father are being chased in a truck through an orchard, a liquid tank on the ground of the orchard is shown on the right of the truck. The view switches to one from the truck and the tank is on the left of the truck. The view switches to outside the truck and the tank is on the right of the truck again.
After Rocky is forced to sign the assignment of rights to his oil parcel to the two goons, he tells Jim he tricked them by signing it left handed. This trick would be unnecessary as any legal document signed under duress (physical or emotional intimidation) is automatically invalid.
During the car chase in the orange orchard, the sound of tires squealing on pavement can be heard, but the entire chase takes place on dirt.
At about 29 mins, when the two goons break into Jim and Rocky's hotel room, the outside and inside layouts don't match. From the outside, you can see two doors, two windows and a painting hanging on a wall when Jim walks inside the room. From the inside, there is only one door, one window and a kitchen where there's is supposed to be a painting. It's clearly obvious that the scene is filmed in one place with two adjoining rooms for the outdoor activity and filmed somewhere else (probably a studio set) for the indoor activity.