Slant sixes are gutless, mine won't pull a loaded 24' enclosed car trailer.
It will pull a 4000lb plus '67 Hemi Charger on a 2000lb trailer and it's pulled a 5500lb John Deere tractor on the same trailer before.
Then again, I did upgrade to a 2bbl Super Six BBD so I cheated. It gets 20mpg hwy @65mph where my old 318 would only do 17mpg. If your going to V8 it, why not go 440? Compared to a big block, small blocks are gutless! Remember, everything is relative.