Many 6 cylinder Ravs came from the factory with the tow prep package. This included a slightly larger radiator, stronger alternator, and other things to bring the towing capacity to 3500 lbs. According to the Rav4 forums if you look inside the fuse box cover under the hood and the fuse location for the alternator is labelled 140A, it has tow prep.
Search Toyota RAV4 Questions
Toyota RAV4 Experts