You have a few things against you

Empty bed of pickup truck is one thing, if its stock it is oversprung to get its 1/2 ton rating

Tire pressure, tires are the first to encounter bumps, so good high pressure on paved roads is great for MPG and tire wear but sucks when you encounter "washboard" bumps

Shocks, most are stiffer so a vehicle won't lean too much when cornering and also have a slow recovery rate
Slow recovery rate means when you encounter many bumps in a row the shock basically turns into an iron bar, lol, so springs can no longer do their job.


The pickup truck effect means load some weight into the bed or change the rear leaf springs to ones rated for empty bed weight and add overload springs, which don't touch the frame until there is weight added to the bed, so you get a good empty bed ride but can still handle the 1/2 ton load

If you will be traveling a longer distance "off-road" then buy a 12volt air compressor and let the air out of the tires for the off-road trek, 20psi or lower, depending on the tire and wheel.

You can get adjustable shocks, you can run them soft for faster recovery off-road and then harder when back on the road so less "roll" when cornering

 

Yeah pickups and washboard roads don't exactly get along. Like Ron said lowering tire pressure can help alot. I drive my truck on some hard pack sand roads that are insane after a rain storm. Dropping my pressure to 15-20psi makes a huge difference but never drive like that on the pavement. Also there always tends to be a perfect speed for driving washboards that matches the frequency of the bumps. I'd never suggest driving beyond your comfort level but try to vary your speed and see where its worst and where its tolerable. There's no speed limits on the roads I drive and I've had my truck up to 70 on them and at that point it just floats over it, BUT I'm left driving like a dirt track sprint car steering into turns letting my rear end kick out lol. Not recommended!