Ram Body Builders guide shows the 2500 6.4 hemi has quite a bit more GVWR payload on certain models and the 5.7 has about the same on other models.
Also the 2500 6.4 hemi has a 10k gvwr and 6500 rawr 11.5" AAM axle.
The 2500 5.7 Hemi has a 9000 gvwr and smaller 6000 rawr 10.5" AAM axle.
Gotta' keep in mind those yellow sticker payloads are GVWR based and the 5.7 hemi with lighter weight tranny...front and rear axle will have more gvwr payload.
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On the subject of vehicle mfg weight specs does anyone have a link to the old '00 to 2019 Fleet Ford truck specs that gave all the mechanical specs. All I find now is Ford trucks new website that only shows 2014 to 2019 Ford trucks.