If you get the RPO codes out the glove compartment, it should tell you what gears it has. My kid's has 3.73s.
GT4 is 3.73 GU6 is 3.42.
AG2 -- 6-WAY Passenger seat
B35 -- Rear carpet floor mat
B39 -- Carpeted floor
B71 -- Wheel well moulding
B85 -- Body side moulding
C5I -- GVW RATING, 8050 LBS
C5M -- GVW RATING, 6100 LBS
C5P -- GVW RATING, 6250 LBS
C5Q -- GVW RATING, 6300 LBS
C5R -- GVW RATING, 5800 LBS
C5S -- GVW RATING, 6600 LBS
C5U -- GVW, 6800 LBS
C5Z -- GVW, 7200 LBS
C6P -- GVW RATING, 8600 LBS/3900 KG
C6U -- GVW RATING, 9000 LBS
C6W -- GVW RATING, 9200 LBS
C7A -- GVW RATING, 10000 LBS
DD0 -- Left & rt heated power mirror
DF5 -- Inside mirror compass/outside temp
FG5 -- Delco/Bilstein gas shocks
F44 -- CHASSIS, HEAVY DUTY
F60 -- SPRING FRONT, HD
GQ1 -- AXLE REAR, STD RATIO
GT4 -- AXLE REAR, 3.73 RATIO
GT5 -- AXLE REAR, 4.10 RATIO
GU4 -- AXLE REAR, 3.08 RATIO
GU5 -- AXLE REAR, 3.23 RATIO
GU6 -- AXLE REAR, 3.42 RATIO
G80 -- AXLE REAR, LIMITED SLIP (POSITRACTION)
HC4 -- AXLE REAR, 4.56 RATIO
JB6 -- BRAKE, POWER, DISC/DRUM 7200 LBS
JB8 -- BRAKE, POWER, DISC/DRUM 10000 LBS
JD5 -- DUAL POWER, DISC/DRUM 6400 LBS
JD7 -- BRAKE, HYD POWER, DISC/DRUM 8400 LBS
KA1 -- Heated leather bucket seats
KNP -- HD TRANSMISSION COOLING
K05 -- HEATER, ENGINE BLOCK
K34 -- CRUISE CONTROL, AUT0MATIC, ELECTRONIC
K47 -- AIR CLEANER, HIGH CAPACITY
K60 -- GENERATOR, 100 AMP
K68 -- GENERATOR, 105 AMP
KW2 -- GENERATOR, 124 AMP
KC4 -- COOLING SYSTEM, ENGINE OIL
L49 -- ENGINE, DIESEL, 8 CYL, 6.5L
L56 -- ENGINE, DIESEL, 8 CYL, 6.5L, TURB0
L57 -- ENGINE, DIESEL, 8 CYL, 6.5L, HO
L65 -- ENGINE, DIESEL, 8 CYL, 6.5L. TURB0, HO
L76 -- ENGINE, DIESEL, 8 CYL, 6.6L, V8, DI, TURB0, ISUZU
LH6 -- ENGINE, DIESEL, 8 CYL, 6.2L
MM4 -- MERCHANDIZED TRANS, MAN 4 SPD PROVISIONS
MT1 -- TRANSMISSION, AUTO 4 SPD, HMD, THM R2 (4L80-E)
MW3 -- TRANSMISSION, MAN 5 SPD, NVG, 109MM,, 5.61 1ST, O/D
MX0 -- TRANSMISSON, AUTO PROVISIONS, O/D
M20 -- TRANSMISSION, MAN 4 SPD, 117MM, 6.55 1ST
M30 -- TRANSMISSION, AUTO 4 SPD, HMD, 4L60-E, ELECTRONIC
NA1 -- EMISSION SYSTEM, GVW < 8500 LBS
NA5 -- EMISSION SYSTEM, FEDERAL, TIER O
NB8 -- EMISSION SYSTEM, CA/NY/MA/CT EMISSIONS OVERRIDE (REQ FE9)
NC7 -- FEDERAL EMMISIONS OVERRIDE (REQ YF5 OR NG1)
NF2 -- EMISSION SYSTEM, FEDERAL TIER 1
NG1 -- EMISSION SYSTEM, NY/MA/CT
NG5 -- REGISTRATION, EMISSION SYSTEM (50 STATE)
NK3 -- STEERING WHEEL, SPORT, SOFT RIM, SIMULATED LEATHER
NP1 -- TRANSFER CASE, ELECTRONIC SHIFT CONT, TWO-SPEED
NP5 -- STEERING WHEEL, LEATHER WRAPPED
NRQ -- EXHAUST, CLOSE COUPLED
PF4 -- WHEEL, 16x7 ALUMINUM
PO6 -- RALLY WHEEL/TRIM RING
RO4 -- WHEEL, SINGLE RR
RO5 -- WHEEL DUAL RR
MSL -- Mexico city code
UG1 -- 3 channel homelink
X88 -- Chevrolet
ZM9 -- Suburban comfort package
11U -- Primary color metallic peweter
13I -- Lt grey interior
132 -- Leather
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AAB - MEMORY PACKAGE
AE7 - SPLIT BENCH RECLINING FRT SEAT
AG1 - 6-WAY POWER DRIVER SEAT
AG2 - 6-WAY POWER DRIVER & PASS SEATS
AG9 - 6-WAY POWER SEAT
AJ1 - DEEP TINTED GLASS
AJ3 - DRIVER'S SIDE AIRBAG (SIR)
AK5 - DRIVER & PASSENGER SUPPLEMENTAL INFLATABLE RESTRAINT SYSTEM
AM7 - FOLDING REAR SEAT
AN3 - FRONT BUCKETS WITH POWER ADJ.
A07 - BODY GLASS - 6 WINDOWS
A08 - RH SIDE BODY GLASS-2 WINDOW **7 - SWING OUT LH SIDE BODY GLASS **8 - SWING OUT REAR DOOR GLASS **9 - SWING OUT SIDE DR GLASS
APD - BELT PROVISIONS-BENCH SEATS
AR7 - FRONT BUCKET SEAT-STANDARD
AR9 - BUCKET SEATS WITH LEATHER TRIMMED SEATING SURFACES
AS3 - CENTER AND REAR SEATS
AT5 - CENTER SEAT
AU0 - KEYLESS REMOTE DOOR LOCK AND TRUNK OPENER
AU3 - POWER DOOR LOCK SYSTEM
AU6 - REMOTE TAILGATE RELEASE
AXP - MPV VIN IDENT POSITION
A20 - SWING OUT QUARTER WINDOWS
A28 - SLIDING REAR WINDOW
A31 - POWER WINDOWS
A52 - FRONT BENCH SEAT
A95 - 6-WAY POWER BUCKET SEATS
BAG - EXPORT PARTS PACKAGING
BGR - BOWLING GREEN PLANT
BVE - SIDE RUNNINGBOARD STEPS
B3J - Fleet Incintive; Kleinfelder Group
B3P - BAILMENT COMMERCIAL ORDERS
B30 - WHEEL HOUSING & FLOOR CARPETING
B32 - FRONT COLOR-KEYED FLOOR MATS
B33 - REAR COLOR KEYED FLOOR MATS
B35 - Covering Rear; FLOOR MATS CARPETED Insert
B37 - COLOR-KEYED FLOOR MATS FOR FRONT AND CENTER SEAT
B38 - FULL FRT & REAR FLR COVERING
B39 - COLOR KEYED FLOOR MATS/ CARPETED
B58 - COLOR-KEYED FLOOR MATS, CARPETED
B71 - WHEEL OPENING FLARES CMD - ASSEMBLY PLANT - FLINT, MI
B84 - BODY SIDE MOLDINGS
B85 - BRIGHT BODY SIDE MOLDINGS
B96 - WHEEL OPENING MOLDINGS
CJ2 - AIR CONDITIONING-ELECTRONIC DUAL ZONE
CJ3 - AIR COND., DUAL ZONE MANUAL
CMD - ASSEMBLY PLANT-FLINT, MI
C25 - REAR WINDOW WASHER & WIPER
C3F - GVW RATING - 7,700 LBS
C36 - REAR HEATER
C49 - ELECTRIC REAR WINDOW DEFOGGER
C5B - 15,000 LB GVW RATING
C5I - 8,050 LB GVW RATING
C5S - 6,600 LB GVW RATING
C5U - 6,800 LB GVW RATING
C5Z - 7,200 LB GVW RATING
C6P - 8,600 LB GVW RATING
C6W - 9,200 LB GVW RATING
C60 - AIR CONDITIONING WITH AIR FILTRATION SYSTEM
C69 - AIR CONDITIONING-FRONT & REAR
C7A - 10,000 LB GVW RATING
C7I
C7W - GVW RATING - 11,400 LBS
DD0 - ELECTROCHROMIC MIRRORS: ISRV & LH OSRV
DD7 - ELECTROCHROMIC ISRV MIRROR/COMP
DD8 - OSRV
DE2 - EXT FOLDING B-E-L MIRRORS
DF5 - INT R/V MIRROR, LIGHT SENSITIVE W/OUTSIDE TEMP & COMPASS
DH2 - LIGHTED LH & RH VISOR MIRRORS
DK6 - OVERHEAD CONSOLE
DK7 - INTERIOR CUSTOM ROOF CONSOLE
DL5 - ROADSIDE SERVICE INFORMATION DECAL
DL8 - DUAL PWR HEATED OSRV MIRRORS
DPF - OSRV RETRACTABLE CAMPER STYLE POWER MIRRORS W/TURN SIGNAL AND HEAT
DR2 - MIRROR O/S ELECTRIC, HEATED DRIVER SIDE ELECTROCHROMIC WITH DUAL GROUND ILLUMINATION
DT4 - ASHTRAY MUFFIN
D07 - CUSTOM FRONT FLOOR CONSOLE
D44 - EXTERIOR BELOW-EYE-LINE MIRRORS - PAINTED FE9
D48 - ELECTRIC EXTERIOR MIRRORS
D55 - CONSOLE
EF1 - DELETE REAR BUMPER
EXP - EXPORT ORDER
EVA - EVAP EMISSION REQUIREMENT
E2C - ORDER TO DELIVERY - EXPEDITE
E23 - 9,500 LB GVW RATING
E24 - DOOR SIDE CARGO, HINGED
E55 - BODY STYLE TAILGATE
E63 - FLEETSIDE BODY
FE4 - RIDE & HANDLING SUSPENSION SYSTEM
FE9 - FEDERAL/NY/MA/ME/VT EMISSIONS
FF6 - TORSION BAR SPRING ADJUSTMENT
FF7 - TORSION BAR SPRING ADJUSTMENT
FF8
FF9
FK2 - TORSION BAR SPRING ADJUSTMENT
FK3 - TORSION BAR SPRING ADJUSTMENT
FLT - FLEET PROCESSING
FT2 - ARM TORS BAR SPRING ADJ
FT3 - ARM TORS BAR SPRING ADJ
F44 - HEAVY DUTY CHASSIS EQUIPMENT
F60 - HEAVY DUTY FRONT SPRINGS
GK9 - REAR AXLE - 4.63 RATIO
GMC - ASSEMBLY PLANT-GM TRUCK & COACH
GT4 - REAR AXLE - 3.73 RATIO
GT5 - REAR AXLE - 4.10 RATIO
GU6 - REAR AXLE - 3.42 RATIO
G65 - LEVEL CONTROL MAN,SELF AD