I havent diagnosed the problem yet but my drivers side HID light is brighter than the passenger side. I'm going to first try swapping bulbs to see if that's the issue. If not, then I'll try swapping the balasts. If that doesn't work and the drivers side is still brighter, than what else could it be that would be causing the passenger side to be not as bright?

 

Do as you plan, if that doesn't sort it out (I suspect it will) you should probably relay the headlights.

 

Generally ballasts either work or not. All HID bulbs lose brightness over time, the 55w moreso than the 35w.

It's probablyy time to replace your bulbs.

Here's a chart to give you an idea of lost brightness output over time.