Mi2bugz, yes either truck you're looking at will tow/haul the same load from a chassis standpoint. You need to research "book" capacities compared to real capacities.
Since you don't understand much mechanically speaking, know that the "book" ratings for payload and axles are typically the absolute most conservative ratings imaginable. And VERY under rated for 3/4 ton trucks.
Do you think the diesel actually has that much less capability for payload than the gasser? Engine is in front, payload goes in the back. They're almost mutually exclusive based on where the weight is in the truck.