GPCM = glowplug control module
ecm = engine control module
tcm =trans control module
bcm = body control module (the thing that basically runs the whole truck, lights, door locks, windows, steering wheel controls etc)
DDM = drivers door module (the driver side window switch assembly that controls the mirrors, windows, etc)
PDM = passenger door module
HSM/MSM = heated seat module/memory seat module
IPC = instrument panel cluster
TCSM = transfer case shift module
EBCM = electronic brake control module (ie, the ABS computer)
SDM = sensory diagnostic module (ie, the airbag computer)
RSA= rear seat audio (the controls for the back passengers)
CDX = cd changer
RSE = rear seat entertainment (ie, the factory dvd player)
VCIM = vehicle communications integrated module (ie, the onstar box)
DRR =digital radio receiver (ie, the XM box)
TBCM = trailter brake control module
ESC = electronic suspension control (ie, autoride on the escalades and denali's)
theres a couple others that Im forgettting, but those are most of them
ben