I have not towed a Ranger so I can't give first hand information like Syd.
I have talked with the customer service center (1-800-228-2481 ) at REMCO Towing (http://www.remcoindustries.com/Towing/Store.php
) several times in the past and found them to be very helpful, knowledgeable and willing to answer questions about towing a vehicle. I have spoken with a customer service representative at REMCO Towing about the 55 MPH limit on towing a 2WD Ranger. He explained that Ford has had this towing restriction in place for several years and that it was imposed to prevent damage to the drive train. He also pointed out that the battery may run down during towing and one must stop every few hours and run the engine to recharge the battery.
I have learned that manufacturers provide warnings for many different reasons. Many times it reflects a very minor risk that requires numerous conditions to exist before that risk is realized. When I finally chose a toad I went with one that only had the restriction of not driving over 65 mph.