Well Sam it depends on a lot of issues, amount of highway driving, off road use (4 WHEEL DRIVE), miles driven, vehicle loads etc.... Being a 02 Chevy and your use of our quick lube centers I would be shocked if you haven't had it serviced, but since your sure it hasn't been I would highly recommend it's service A.S.A.P! Your Autotrac unit has special fluid which breaks down real quickly under high loads and heat! You state you drive off road and use it a lot and I can guarantee that it needs to be serviced! One reason the Autotrac needs to be serviced on a regular basis is that there is a clutch assembly which is used to transfer power to the front driveshaft, failure to service the unit under severe duty can cost you a lot of money! My recommendation----if you use your 4 wheel drive and pull loads on a regular basis, service the unit every 20,000 miles to prevent any damage due to fluid breakdown! If you only occasionally use the unit, and do not pull heavy loads---Inspect every 20,000 miles for fluid condition and Servicing at 60,000 no matter what! This will save you a lot of money if you plan on keeping your vehicle past the 100,000 mile mark! Thanks Darin!