That looks like way too many LED's. I'm guessing you're looking at a 42" Bar? Just get a standard twin row, 42", combo beam. Although Philips and Osram LED's are some of the most common, CREE LED's actually outperformed them, when used in a combo pattern.
Here's what I found real quick:
The drain back problem is pretty easy to diagnose and fix or live with. When you first crank up, with your foot on the brake, engage the tranny in reverse, if you feel the tranny solidly engage just drive. If not with the engine running put the tranny in neutral...
I have this issue with mine once in a while.
There was a recall for the filter / anti-drainback valve in the trans.
Look into it to see if that has been done on yours, and if not, I'm 99% sure that's the problem.
Just get a pre-made 9005 Harness (you wanna run 9005's in the Fogs, trust me). Wire it up as you normally would, put the Trigger Wire on the Parking Lamp Circuit with a Switch, and you're done.
I still have a ton left from the Discount Cases I got a while ago. You'd be tough to beat the price you can get it for on Ebay, per bottle, if you buy it in Cases.
Summer...
I have no Science Info to add, but I use strictly Howes now. Meaner Power Cleaner in the Summer, and the other stuff in the Winter. My Trucks smoke alot less now, when running Howes, than they did when I was running Power Service.
Now that they're hitting the Lots, anyone seen one around their neck of the woods or driven one?
I'm kinda tempted to go give one a drive and see what they're about.
The diagnostic fee is just so they get paid for doing something, even if they don't discover the problem.
Should you have to pay for their "guess work" in diagnosing the problem, hell no, but that's how it goes.
Best thing I would suggest is to call GM Customer Support, and tell them what is...
Dealers have to do everything "by the book". If they don't and something goes wrong, they'll catch more hell than you can imagine for it.
It's a shitty game, but that's how they gotta play it.
Do you have another Dealer you can go to that isn't too far away? If you have a Chevy, try a GMC...