My wife drove my mostly stock 59 Suburban with a 307 V8 and an SM420 on a 2500+ mile trip from California to Tennessee. It was towing a Datsun 510 station wagon. Both vehicles were loaded to the roof with everything we owned when we escaped from the People's Republic. She was following me as I drove a 1970 Cadillac Fleetwood and towed an 18 foot 3 axle backhoe trailer. The Caddy/trailer combo weighed 16,700 pounds. It got 5 MPG, and the Burb got 10. Drive 100 miles, gas up, "rinse and repeat!" It took nearly a week to get back to Tennessee.