I have a stock front bumper on my XJ with Detours Offroad's "Bumper Brow" now I have a set of 6" Daylighters on it, & the lights seem to move about ever so slightly making them uneven and REALLY Annoying. Now they appear very tight but the still move about slightly & with limited space I can't tell if I am doing something wrong.

 

You need a steel bumper with light tabs.

 

If it's still bouncing around a lot on you. I removed the washers that came with the kit and pick up some thicker 1/2 inch washers and snugged it up good and tight. If you can move them with your hand then their not tight enough. Then I'd check the bumper to make sure it's not flexing. The bumpers are cheap steel. The weight of the light maybe flexing the steel as your hitting bumps down the road.