You need shocks with bypasses to help keep them cool and stop shock fade on the washboards. I hear a "flutter stack" valving also helps.
I'd call downsouth Motorsports and give them a budget, tell them your needs, your evironment, and ask if Sonny can custom valve them for you.
They have the best customer support I've ever known, they send parts all over the world, rebuild shocks, and Sonny is a good guy in general. I've seen some of their test hits in the desert thru high speed rythm sections on YouTube, and even a guy in Iceland doing the crazy ass Icelandic formula off-road Hill climbs with shocks that Sonny built.
Normally free shipping too.
https://downsouthmotorsports.com