Factual error: At the end when Joe, Brandy, Clem and Charlene, the alligator woman are in Joe's 1967 Plymouth GTX, Robby claims his car is faster. Charlene chides back about his Trans Am, saying 'you think you can match that little old slant six against his 426 Hemi?" Pontiac Trans-Am's did not come with slant sixes, a Dodge motor. His was obviously a V-8, and would have most likely have been a 400, but we get the 'yours is really small' reference.
Factual error: When Joe is at the dealership talking about the Rambler, the dealer says they came with a 289 automatic with 3 on the tree. It is impossible to have both an automatic transmission and a "3 on the tree" which is a manual transmission, at the same time.
Factual error: In the scene where Joe Dirt is talking to the sales rep at the dealership about who ordered the Rambler wagon, the sales rep mentions it came with a 258 cubic inch engine. No Rambler ever came with the 258 six. American Motors (makers of the Rambler line) came out with the 258 in 1971, 2 years after the last car with the Rambler name (the Rambler American), was sold in 1969. Although I was impressed that they bothered to mention an actual American Motors engine, it's still not correct.