5ver or TT doesn’t really matter in how well the truck handles the load from a power standpoint. Frontal area, weight and driving conditions are far more important.
And IMO driving conditions is what I’d rate highest concern for gas vs diesel.
Mountains, altitude, nasty head winds common? I wouldn’t want to pull with your current truck. Truck will handle it, but not at the speed of level of effort out of the truck that I’d prefer.
Mostly flat-ish, low altitude, not out in the plains where the wind blows sideways for hours on end? I wouldn’t hesitate to just rock the old Hemi, especially if I already owned it.