I apologize, I meant Rough Country. They offer a spacer kit designed for the Trail Boss. The spacer lift fits on top of the front coil springs, whereas the block is bolted below the strut. Same result, but in a different way. Seeing as the trail boss already comes from factory with a lift, I would not recommend the block method. Ultimately the best way to achieve a leveled lift is with front height adjustable shocks, like Bilstein 5100s. But they are not available yet...
here is the link to the rough country 1.5" trail boss kit:
https://www.roughcountry.com/gmc-leveling-lift-kit-1319.html?find=2019-chevy-silverado-1500-4wd-381258