With a few exceptions, 3/4 & 1 ton trucks are nearly identical. In particular, motor & transmissions.
Tow rating is mostly about the motor & transmission. They don't make different lower rated motors & transmissions for 3/4 ton trucks...the result is pulling power is pretty much the same.
Cargo capacity is mostly about springs, suspension and wheels. Regardless of engine, they are the same, so the heavier diesel works against you as it eats up capacity.
In terms of real life towing, you can usually tow more with a bumper pull as hitch weights are typically 10-15% of trailer GVW. The result is the tow rating often is the limiting factor. If you go with a 5th wheel, pin weights are typically 20-25% and cargo capacity often is the limiting factor.
