In 2002, the Avalanche is a child to the Suburban.
Interior - A pillars to just in front of the C pillars is all carryover Suburban (except Cargo/Fog switch, TNF cluster, RH body harness). Cargo/Fog switch looks the same, but the pinout is different.
Exterior - Front end sheet metal outers were new, hood is new, rear end sheet metal mostly new (except for bracing). Doors (including mirrors) are carry over suburban, with new skins (holes for cladding). Roof is new, sunroof is carryover. Frame, engine, suspension and hitch is Suburban.
All exterior lighting is new (except neon CHMSL - carry over modified harness from Blazer/Envoy).
Escalade EXT is an Avalanche with Escalade front end. New rear bumper and tail lamps. New LH body and chassis harnesses. Rear Park Assist and Real Time Damping modules are Escalade, but packaged under the rear seat (and software changes).
Note - These vehicles are all based on the GMT800 platform. Many common parts between vehicles. Many parts are carry over, but modified slightly to work with other vehicles.
Hope that makes sense / helps...
