I had the same problems with Gorillas and because of the cost for me to switch to summer bros and also needing the stock cv's I decided to make them work. If you can get the Gorillas to stay in they are great axles.
First you need to call the company that makes that long travel kit and find out what axle shaft lengths they use. A +6 is kind of generic and you will find that axle lengths are different an most +6 kits. Verify that your Gorillas are the right length. Gorilla Axle will cut you any axle length you need for like 90 bucks.
You can also try using the GIS thing. Its this clip that goes in the differential between the axles and hold them together. Gorilla Axles has them. I have heard mixed reviews on whether that solves the popping out problem.
Last thing is to bolt those bad boys together.. Thats the route I went and two seasons later they never popped out again. Look up "I'm bolting my rear axles together" on the rhinoforums.net under technical/suspension and you'll see my thread with pics and details on this. Sorry but I can't post urls yet on this forum.