Hi. There are c-clips that hold in the axles. You need to remove the rear diff cover. Then there is a pin held in by a 3/8 bolt. Remove the bolt and slide the pin out. If it is a posi rear end there will be an "S" clip that has to be removed. Once that is removed, or if it was never there, you will see a c-clip on each side of the pinion gears. Just push the axles in a bit, and pull the clip out. Then the axle slides right out. I'll try and attach a section from the shop manual also.
WARNING: The electrical power to the air suspension system must be shut off prior to hoisting, jacking or towing an air suspension vehicle. This can be accomplished by turning off the air suspension switch located in the RH kick panel area. Failure to do so can result in unexpected inflation or deflation of the air springs, which can result in shifting of the vehicle during these operations.
CAUTION: Do not damage the rubber O-rings in the axle shaft grooves.
CAUTION: Do not damage the wheel bearing oil seal (1177).
I checked all the rear end options for your truck. Your rear end does have posi but it doesn't use the spring I was talking about. It has clutch backs in the side spider gears. I will send pictures of the procedure.