2002 Chevy 4wd
maby im wrong but if you rev up and only rear wheels spin that means that it might be 4 wheel drive but not constant 4 wheel drive or diff lock system ,,,, ,, in 4 wheel drive all wheells will turn together but if pressure of slip is bad enough or torque high enough only 2 wheels will drive ,,, thats why diff lock locks wheels together in each axle to over come this ,,, all wheel drive like in landrover locks all 4 wheels together to ensure all wheels rotate to give best grip