Maybe i can help.
Make sure your spindles are positioned correctly. The axle and cv joint need to be closer to the bottom of the car (you would think it would make sense to be the other way, but its not).
Also, here are the lengths of what the axle shafts are for the rear end for our +3 kits. This is total length, end to end. only way to measure it, is to pull them out of the cv joints completely
05-07 Years. Driver side= 19.38" Passenger side= 20.60"
If you have an 08 or newer: Driver side= 18.97" Pass side= 20.93"
Also, i would double check the length of your rear shocks. The longest they can be when fully extended are 15.47" eye to eye. If they are longer, the cv will start to go beyond its max angle, and damage will result.
If everything is correct.. i would suspect that possibly the balls, cv cage, or outer cv joint cup is damaged, and not allowing the axle to plunge in the joint. The stock cv joints don't require a lot of pressure to pop them out of the diff, so make sure the cv joint rotates, and plunges smooth. The diff side joint is the one that plunges. The outer joint is fixed.
If that all seems good, then possibly the clip that holds the joint inside the diff is damaged, bent, or not seating correctly. Or the splines on the joint or inside your diff has been damaged from it popping out or something, and not allowing the clip to perform its job.
You can also pop off the shock, and sway bar end link, and cycle the wheel through the travel, and make sure the joint doesn't want to pull out. also, spin the tire around as you move it up and down to make sure there is no binding. Keep in mind, if you go below the shock travel, it will bind, so i like to put an adjustable tie down in the shock mount eyes on the chassis and a-arm, so you know it can't go lower than that 15.47" measurement.
Feel free to give me a call if you need more help. 800-457-7223 ext 228.