Off-road enthusiasts have been clamoring for years for GM to produce a body-on-frame SUV to do battle with the Jeep Wrangler and Ford Bronco in the narrow niche of off-road SUVs from American brands.

Before it got turned into a modern-day GMC Jimmy, this truck used to be a very conventional 2022 Sierra 1500 Regular Cab model. What followed was a highly elaborate conversion process that resulted in ...