I could not kill the 351M in my '80 F250. It got 10mpg loaded or empty and it took a pounding as a combination tow-truck, with a hydraulic sling tow on the back, and an 8 foot Fischer plow on the front in the winter. Never had a problem with the motor or the C6 tranny. Only thing that ever happened that was serious was breaking the driver's side axle housing at the leaf spring mount. One day, even, I had a guy walk up to the shop on a cold winter day....it was at least -10 to -15*F... his diesel truck froze up a couple hundred yards down the road. I went down with my heavy chain and hooked it up to his KW, with a loaded 53' reefer hooked on it, cranked the old Ford into low range and pulled it up a 3-4% grade into the lot so we could warm it up. Every full revolution of the tires left a 1/2 revolution squeal but we made it, even though the idiot dumped the clutch just shy of the crest of the hill to try and fire up his engine.