Daryl, I recently went thru your decision process.
Here's what I did.
Bought a used PJ 20' 20K gooseneck dump trailer, dual axle, dual wheels each axle, (8000 lbs empty) because I have free dirt/road material immediately adjacent to my place on neighbor's property. Dump is hydraulic pump driven by HUMONGOUS 12V battery. Battery will handle 4 dumps before needing recharge.
My F350 gasser, small v8 manual transmission will not pull it around on the ranch loaded, much less on the road. Insufficient traction, burns clutch, wheels spin. I mean, it will NOT pull the load.
Studied new vehicles, Toyota Tundra has awesome pulling power, was considering it. Then found a used Ford 350 6.7L diesel dually crew cab on Craig's list just a couple of miles away which was in superb shape. Bought it for 1/5 cost of new Toyota.
Here's what I've learned:
Used is WAY cheaper.
Gooseneck is the only way to go for such heavy loads. Just trust me.
Trailer brakes and brake controller is mandatory.
The trailer is larger/longer than I need to just haul dirt... but it'll haul my tractor, other stuff too, so length is good for me.
First trip to a pit to get material, I got two scoops of their bucket = 18000 lbs... yep.. 9 tons
Don't lecture me about being overweight... it was a learning experience.
The dump trailer hydraulics will lift whatever the trailer is qualified for, in my case, 20000 lbs.
I loaded a 60% bigger mound of dirt into my trailer from the neighbor... lift would barely, barely lift the bed to dump, almost burned out the pump that time, had to wait for it to cool down several times.
Lesson...what looks like a tiny amount of dirt in the trailer bed and on the ground is amazingly heavy... extremely easy to get overloaded. I mean extremely easy.
Getting the largest weight capacity trailer is key if you are going to be doing much hauling at all..but high capacity does not dictate a big trailer.
The dually pickup wheels, IMHO, are required for hauling such a load, as is a 1 ton pickup (issues with springs, etc.)
I WISH I HAD FOUND A 4X4 DUALLY. The extra traction and speed control would make an ideal rig for my needs. As it is, when in the pasture which is rutted, bumpy, shallow inclines and dips, I find myself wishing for 4 wheel drive ... but I'm getting along by babying the clutch. Backing is worse than forward in the pasture. Net... hauling at road speed is only part of the discussion... being able to deliver the immense load exactly where you need it to the pature is equally key. If your delivery point is now and ever will be flat stable ground, not slick, then perhaps you can put less signifigance on slow speed traction with dirt conditions.
If you have never driven a diesel with a truly heavy load under pasture conditions, there is no way you can truly appreciate the wonderful low RPM lugging capability it provides. Maybe a gas engine if a dually 4wd would work also, never had one so I am not an authority.
So, do the math for your situation... trailer purchase, pickup purchase, brake controller, outfit pickup to charge trailer while driving (GOTTA use 00 wire IMHO, which is truly costly), trailer ramps, great battery charger for overnight charging divided by number of loaded trips, and factor in what other uses trailer and pickup have for you....