Who said the jeep is only true American sports car?

There's no widely known or documented quote attributing the statement "the Jeep is the only true American sports car" to a specific person. It's possible you've misheard or misremembered the quote, or it's a less-known opinion expressed informally. While some might argue a Jeep's off-road capabilities could be considered a form of sporting performance, it's not a generally accepted view that it's the *only* true American sports car.