Update: found another source for GM RPO codes and now have almost all of my codes figured out, i still have a few to find and would appreciate any additional sources or info.
GM RPO codes :
http://www.rpocodes.com/GM-RPO-codes/gmrpocodes0through4.htmlAS3 - seat, right rear, suburban
A52 - seat, front bench
BS4 - INSULATION, BACK PNL
BY1 - ORNAMENTATION, EXTR EMBLEM, BODY, VAR 3
B85 - Extra molding, Belt reveal
B96 - Extra Molding, Wheel opening
CD4 - Wiper system, pulse
C6W - GVW RATING, 9200 LBS
C60 - Air conditioning, front manual controls
C91 - Lamp, interior courtesy
D1Z - GEAR, SPEEDO DRIVEN (D1Z)
D44 - Mirror, outside painted
E5Z - SPEEDOMETER ADAPTER (DELETE)
E6J - ?
E63 - Pickup box, fleetside
E9Z - SPEEDOMETER KEY (DELETE)
FLT - ?
GT5 - Rear axle, 4.10 ratio
G80 - axle, rear, limited slip
JAN - ?
JB8 - BRAKE, POWER, DISC, DRUM 10000 LB
KC4 - Engine, Oil cooler system
K19 - Air injection reactor system
K22 - Generator, 94 amp
L19 - Engine, 7.4L V8 TBI
MX1 - MERCHANDISED, TRANS, AUTO PROVISIONS
M40 - Transmission, Auto, 3 speed, Torque Conv. Var. 1
NA5 - Emission system, federal requirements
NL2 - Fuel tank, auxiliary
NY7 - Transfer case, shield (skid plate)
R04 - WHEEL SINGLE RR
TP2 - Battery, auxiliary camper
UA1 - Battery, high capacity
UM7 - Radio, AM/FM, Seek/Scan, Clock ETR
UN9 - RADIO, SUPPRESSION EQUIPMENT
UP8 - STEREO RADIO INSTALLMENT PROVISIONS
U73 - Fixed Mast antenna
VQ1 - ?
V02 - Radiator, Heavy duty w/trans. oil cooler
V73 - VEHICLE STATEMENT, USA/CANADA
V76 - front hook towing device
WAM - ?
XYN - LT235/85R16E, R/PE, ST TL ALS BL FRONT
YD3 - FRONT AXLE, BASE EQUIPMENT FOR SCHEDULING, GVW PLATE
YD6 - REAR SPRING, BASE EQUIPMENT
YG3 - ORNAMENTATION, BODY, SIDE, 6 WHL OPENING BRIGHT
YK6 - ?
YYN - LT235/85R16E, R/PE ST TL ALS BL REAR
ZN3 - ?
ZY5 - COLOR COMBINATION, EXTERIOR DECOR
12L - SECONDARY COLOR, EXTERIOR, SILVER MET (91)
6F6 - ?
72U - PRIMARY COLOR, EXTERIOR, MED GARNET RED MET (91)
73A - STRIPE COLOR, ACCENT, TWO TONE, VERMILLION/CARMINE
77I - INTERIOR TRIM, DK MAPLE (I)
77W - TRIM COMBINATION, DK MAPLE (W)