The load was actually pretty stout. On a dynojet 224xlc you can load it up to where the truck cant pull through it, which is what Coltons did at first. A big single turbo takes rpms to generate enough drive to get the turbo lit. Once they got the load dialed in right and he started at enough rpm to build boost and pull through it, itd go. Big single turbos are not very forgiving on a dyno because you generally start in overdrive with no boost built and the converter locked, so you don't have as much give to pull against to get some drive going. On the street the turbo wont seem as laggy as you can run through a lower gear faster and hit the next gear with boost and power already built, to keep the charger lit.
Id suspect the only way hell see big fuel only numbers on a dyno would be to run on a Superflow where he can start at a max rpm and pull backwards against it. Or start the run in direct and let it run through that gear and hit overdrive. Youll have to ignore the shift spike and read the correct gear ratio since the run will have 2 different ratios, but it will hit overdrive with boost already built instead of starting without it.