From the magazine:
John Kennedy Loyal, Wisconsin
Vehicle: 2002 Chevrolet Silverado 2500HD
Driver Experience: Dyno, drag, tow, pull, wrench
Engine: 7.1L Duramax (1,200 hp and 1,500 lb-ft)
Turbos: Custom Maximized Performance race twins, BD Intercooler
Electronics: Kennedy Diesel race tune
Injection System: Kennedy Diesel twin lift pumps, Wicked CP3 mounted with MPI dual fueler kit, Kennedy race injectors
Injectables: Custom nitrous and water-methanol systems
Intake/Exhaust System: MPI intake and Kennedy Diesel 5-inch exhaust
Transmission: Allison 1000 built by Inglewood Transmission with a Sun Coast converter
Suspension: Stock
Tires: 285/75R16 BFGoodrich
Wheels: 16-inch Centerline
Differential: Front and rear lockers with 3.73 gears

"7.1L"??? Is this something to do with a different stroke?

I don't subscribe to the magazine (most mags don't have much about the 6.5 anymore), but I'll find it locally and buy the issue, just to vote!