My sirio has slipped a time or two but not bad. It's snug enough to stay in place driving down the road but will slip when it hits a low branch which is kind of good really.
My P5000 is permanently mounted to the top of my 97 Ram 1500 4x4. Glad that the pivot at the base moves under stress...this has probably saved my roof from tearing the mount out. I have had no problems going down he road at 75+ and it moving however. Yesterday i was backing in to a spot with low branches and thought the whip would take it but I must have miscalculated because I looked out of the top of my windshield and saw my whip laying down. I keep mine as hand tight as possible but is will still give when need be. You might have something going on if it leans back just going down the road?
You might want to ask them how they plan on shipping your antenna. They shipped my sirio 5000 in a bunch of wrapped up cardboard pieces and about a half of roll of mailing tape. No kidding when it arrived it looked like a banana. I was a little upset at first because I have no idea how it survived the trip from California to Tennessee via The US Mail! I was lucky it wasn't damaged. I'd give them a call and express my concern on the shipping method let them know you want it in tube or some type of box. I'd pay extra if I had to.Just heard back from DNJ. They hope to have the new antennas in about 3 weeks.