When Jim is in the hospital he is confronted by the two guys from the truck that hit him. Both men are handcuffed to each other as if they are both being arrested. While the driver would have been detained for driving while drunk, the passenger would not have, since he had done nothing illegal. The police would have no legal cause to hold the passenger.
After Dr Yost rigged the exhaust in Rockford's rental car causing Rockford to nearly lose consciousness while driving, Rockford jumped out of the car just before it went off the cliff. However, the Lincoln Continental he jumped out of was a recent (1970's) model; the car that flew off the cliff and exploded in the next scene, while the same make/model/color, was clearly an early 1960's model.
Rocky's truck is struck from behind, but after the accident Rocky tells Jim bricks went through the cab as a result of the accident. A vehicle hit from behind would not cause the bricks to go forward toward the cab. After an impact like this the bricks would tend to move backward with respect to the Rocky's truck. This is an example of Newton's First Law of Motion. If Rocky's truck were hit from the front, then the bricks would have moved toward the cab.
When Rocky's truck is hit, just after the shock, you can see the tire they used to protect the truck lying under the bumper. Nevertheless, it must have been quite a shock as we saw the entire bed of the truck moving.
When Jim is driving the big sedan with the tampered exhaust, he gives no indication that there is something wrong with the car. However car exhaust, especially from the over sized cars of that period, would have had a very strong odor. Jim would have known something was wrong long before he started to pass out.
In the hospital Rocky tells Jim that when the other truck rear ended him, a cement block went through the cab and damaged the passenger side window. But when the accident was shown, none of this had happened, showing that the hospital scene was filmed before the crash scene and that they didn't go back to re-shoot the hospital scene to correct it.