I have a Mossberg 500 Turkey Thug 12 gauge with the lightning pump action trigger system...at first mine had a problem with the cartridge stop (it was bent to far out, not letting the shell get on the elevator), but after bending it slightly back, and reassembling/re-oiling it, now it works great.
I also own a Mossberg 835, and it's never gave me any trouble *knock on wood
Some people don't like Mossberg, but I am NOT one of those people. Enjoy the new gun
If its the pistol grip one you might want to reconsider using the red dot. That stock will more than likely put you out of line with the barrel and sights.