The only engine available is the 6. 7L ISB Cummins. 

Why does GM have both Chev and GMC trucks? Sterling is owned by Freightliner ( a div of DC ). This way a customer who deals with Sterling for their "larger" trucks can also get a "smaller" one at the same dealership. Shadrach
I always heard that GMC is just a Chevy with lockwashers!!!