axle ratio

I am looking into purchasing a toy hauler to pull w/ '99 k1500 suburban (5.7 liter). Since the towing capacity varies by the suburban's axle ratio, how do I determine which axle ratio I have? Thanks!

Visit your local GM Dealer, with your VIN # and ask for an original equipment printout. They do it for free and you get a list of everything that the factory installed.

Your rear end is probably around 3.70. Certainly good enough for hauling up to medium weight 20' boats. Much more and you are pretty much out of luck. To change the rear differential, you'd have to match the front one as well.

Do NOT tow in overdrive and if you do not have the tow package add an aftermarket transmission cooler.

Look in your glove box for a list of codes.
You should have a match for one of these listed below.
Most common would be:
GT4 - 3.73
GT5 - 4.10
Gu6 - 3.42

Others listed below:

G72 : AXLE REAR, 2.14 RATIO
G75 : AXLE REAR, 3.62 RATIO
G80 : AXLE POSITRACTION, LIMITED SLIP
G87 : RING GEAR, 8.50 INCH
G89 : RING GEAR, 7.50 INCH
G92 : AXLE REAR RATIO, PERFORMANCE
G9S : AXLE REAR RATIO, ECONOMY
GH0 : AXLE REAR, 3.54 RATIO
GH2 : AXLE REAR, 2.29 RATIO
GH3 : AXLE REAR, 2.77 RATIO
GH4 : AXLE REAR, 2.92 RATIO
GK9 : AXLE REAR, 4.63 RATIO
GL3 : AXLE REAR, 6.17 RATIO
GM1 : AXLE REAR, 2.59 RATIO
GM3 : AXLE REAR, 3.45 RATIO
GM8 : AXLE REAR, 2.56 RATIO
GQ1 : AXLE, STD RATIO
GS4 : AXLE REAR, 3.70 RATIO
GT4 : AXLE REAR, 3.73 RATIO
GT5 : AXLE REAR, 4.10 RATIO
GT7 : AXLE REAR, 3.33 RATIO
GT8 : AXLE REAR, 4.10 RATIO
GTY : AXLE, WIDE TRACK
GU1 : AXLE REAR, 2.41 RATIO
GU2 : AXLE REAR, 2.73 RATIO
GU4 : AXLE REAR, 3.08 RATIO
GU5 : AXLE REAR, 3.23 RATIO
GU6 : AXLE REAR, 3.42 RATIO
GV2 : AXLE REAR, 5.83 RATIO
GV4 : AXLE REAR, 3.36 RATIO
GV8 : AXLE REAR, 2.72 RATIO
GW4 : AXLE REAR, 3.31 RATIO
GW6 : AXLE REAR, 3.27 RATIO
GW9 : AXLE REAR, 2.93 RATIO
GX3 : RATIO,TRANSAXLE FINAL DRIVE 3.33
GYS : RATIO TRANSAXLE FINAL DRIVE 3.65
H04 : AXLE REAR, 4.11 RATIO, SINGLE SPEED
HA3 : AXLE REAR, 5.29 RATIO, SINGLE SPEED
HC4 : AXLE REAR, 4.56 RATIO
HC7 : AXLE REAR, 5.13 RATIO, 7500 LBS, SINGLE SPEED
HC8 : AXLE REAR, 3.21 RATIO, SINGLE SPEED, TRUCK
HE3 : AXLE REAR, 3.07 RATIO, 3500 LBS, SINGLE SPEED,
HF7 : AXLE REAR, 4.56 RATIO, IOOOO LBS, DANA 70, SINGLE
HF8 : AXLE REAR, 4.88 RATIO
HK1 : AXLE REAR, 2.87 RATIO
HK9 : AXLE REAR, 5.86 RATIO 10000 LBS, SINGLE SPEED

Thank you both for the info.. Terryinatlanta that is an impressive list - had just what I needed. Thanks again!