i had a 94 F250 x-cab 4x4 with a 460 (8 foot bed) and loaded it up with cement blocks. don't know the count but it was up to the side of the bedrails. i worked in a mill and pulled it on the scales and it was 3200 lbs. didn't squat it much but i could tell it was there by the ride. motor had no problems.
years before that i had a 92 F150 4x4 loaded with lumber. the 302 barely pulled it and the rear springs were buckled upside down and riding on the bump stops. could barely steer the thing. don't know the weight of that load.