Dyno time. And throw an engine block or some sandbags in the back for traction. It's a pickup after all... Seriously you need weight in the bed while on the rollers. Even then I had the tires screaming.
WarWagon, What type of dyno was this on?
Normally wheel spin is associated with loose straps / improper tie down methods / vehicle placement on rollers improper.
some less practiced or informed dyno operators will loosen straps. it creates more "impressive" results for a dyno printout.
Twin Roller dyno's typically have more tire spin than single roller dynos do. There are way around this to help it a lot if you know what you are doing