The '06 GMC Savana and the '07 GMC Savana share the same 6.0-liter V8 with 300-hp and 360 ft.-lb. of torque. However, the 6.0-liter Vortec 6000 (LQ4) engine comes in a variety of GMC trucks and is tuned differently to fit each application. For example the '06 GMC Yukon Denali was standard with a 6.0-liter V8 tuned to 335-hp. That may explain the different specifications you were seeing. Horsepower differences between engines in the same engine family are commonly attributed to changes in airflow, exhaust, timing, or compression characteristics.