If you want a big truck, my friend's father buy a F-550 crew cab fram and a f-350 double wheel rear box. Ford did that, they cut the fram to thw right size, rebolt the wheel at the right place, change driveshaft for a f-350 drive shaft and put the box on it. SI Is now with a F-550 crew cab pick up with power stroke v8 engine and air suspension.
There about 10-12 truck like this in north america and you keep your warranty if it's done by Ford.