Griswold's vs. Johnson's

Ok so it's blatantly obvious that the idea behind Johnson Family Vacation comes directly from the 1983 classic, National Lampoon's Vacation. I personally haven't seen the film, but am curious to how much they actually borrowed from the original. I know the opening scene is exactly the same. The father and son going to the car dealership to pick up the new car, and their car never came in. There's also a scene similar to Chevy Chase getting naked with Christie Brinkley, however it's Cedric. Another similarity is a highway rivalry with a trucker which sounds exactly like the sequence in Xmas Vacation. Has anyone seen this film, and can comment on what was copied from the timeless original?