Download the manufacturers' towing brochures and compare how they rate the different trucks. It is worth the time to do so.
Engine type, diesel versus gas, makes a difference in towing capacity and so does the trucks gears. With the GM/Chevy heavy duty trucks the highest tow rating is with the diesel trucks which all have the 3.73 gears. With the gas trucks the ones with the 4.10 gears have a 25% higher towing capacity than the same trucks with 3.73 gears. It is a difference of nearly 3,000 lbs. in towing depending upon the gears.
I would look first at the Ford or Chevy trucks in those years and the 1/2 ton models and find out which ones have the greatest towing capacity. If one has the capacity then I would go that route and not get a 3/4 ton truck that will have a harsher ride and will have a base weight that is 2,000 lbs. more than the 1/2 ton pickup.
A lot of the extra capacity of the 3/4 ton truck is eaten up with the 2,000 lb. extra weight of the truck. It also affects fuel economy whether towing or not and the type and cost of the tires that are required.