I'm thinking that you're right on all counts here...
The car isn't overweight...I mean, it's an Abody! Even a V8 big bumper car came in under 3,200, IIRC...that's probably 1000lbs lighter than a 5.9L Grand Cherokee or 1500lbs lighter than a 5.9L Ram. I do have a higher RPM stall so that's probably not it either but there's no doubt that the 2.73 ratio is a big source of the sluggishness. Still, the motor feels like it just doesn't want to rev. Holding it in lower gears helps some but not enough... So yeah timing and carb tuning are certainly contributing.
