Is a GMC truck just a dressed up Chevy truck?

The Chevy and GMCs from 1973 to present are essentially the same. ALL GMCs have used Chevrolet engines since the late 60s.
Didn't Dodge and Fargo have the same fenders, doors and beds? The Plymouth Trail Duster was a Ramcharger with minor differences.
Even look at the Darts and Valiants. The 63-66 doors interchanged. From 67-76, the outer door skin stamping was the same. UNder the skin, despite the 106, 108 or 111 inch wheelbases, these were basically the same chassis.
GM Malibu, Pontiac Tempest, Oldsmobile Cutlass and Buick Skylarks were the same under the skin but up until the early 70s, they even had their own brand of engines. The mid 70s saw a lot of consolidation into the cars. "Corporate" V8s were Chevrolet. Buick built the 3.8 V6, Pontiac had the 2.5 Iron Duke inline 4.
Crossbreeding existed even across import to domestics. Mitsubishi 2.6 and V6 engines in Mopar Minivans, etc.