Like the rest of you, done so much reading and research on these HID kits, it would make your eyes bleed. Purchased the Yukon XL SLT in late Nov, and pulled the trigger on the Opt7 Bolt Series HID kit after seeing many good reviews online. They include all the relays/capacitors, etc that you need, very thorough kit, wiring and connections pretty good, decent instructions, etc.
Didn't start out well...only one bulb worked right out of the box...it flickered a couple times and died. I swapped ballasts and bulbs around to isolate the problem, and it was the HID bulb. Opt7 was very responsive and seemed genuinely concerned...they shipped out replacement HID bulbs and a ballast also. Having become a pro at removing the airbox and bulbs, I dove in again. Well, the first replacement bulb I tried wouldn't even turn on...great. The second one flickered, but then came on and stayed on. Hmm. I again swapped bulbs side to side to make sure the ballasts were ok...everything was working. So, I put everything back together after siliconing the backs of the headlight housings, and drove it. Light ouput is WAY better than stock, huge safety difference!!
Well, three weeks later, and the passenger side bulb is dead. Two nights ago, when leaving a restaurant, the bulb failed to light...however, after our next stop, it came back on and stayed on. Last night, the bulb is totally dead (it had flickered a few times)...I've contacted Opt7 again, we will see what they say. But at this point, I am about done...I can't have my wife and newborn son driving around in a vehicle that the headlights may or may not work in! So unsafe...
So, can't say that I can recommend Opt7 products anymore...when working, they are super bright and work well with the projector housings, but three bulb failures in a little over a month? Not acceptable...