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Stop leak of any kind WILL plug the orifice tube on all GMs. Then you will be in for a nasty repair.

Do you just the 12V power? if yes then have you attached the wire wound up by the brake booster to the stud at the front of the fuse box? Also there was a dummy J-case fuse in some of the fuse boxes on these trucks from the factory.

Did the wires going to stud 1 and 2 in the engine compartment fuse box get reversed? one is for the brake controller and the other is for constant hot.

The ground should also connect to the 7 way plug

There is a backup light feed in he 7 way plug. Read the cover and it will tell you which one.

I would say that you do not have sensors in the wheels that you bought. The sensors used in the '11 and '15 are the same and the air out method should have worked if the sensors were there. The air out method and the re-learn tool basically "wake up" the sensor on command while you have the truck in relearn mode.

Are you sure that you got the right tool from Amazon? The newer trucks use a different frequency!

Yes it was working and still is even with the hellas added

I put Hella horns on my '10 silverado. I just used the horn wire in the front of the truck as the signal for the relay straight from the battery. Worked just fine.

Canadian law is DRL is on when out of park. If there are no dedicated DRLs then the low beams must come on. Usually if you start the truck and do not put it out of park, you can turn them off by turning the auto lights to off momentarily. When you then go put of park the light will come back on.

If you already have the Power mirrors, then the signal wire is already in the bundle and it should be plug and play

Just the relay harness.

I just used the relay harness on my 2010. It works fine with no messages on the dash. Being in Canada I also have my lows as DRLs and they run all the time. You will get flicker without the relay harness.

can you not get at it through the bacj and compress the locking tabs seeing as how it is off the truck. Alternately remove the retainer and take the whole piece out to remove the lock.

My 2010 4.8 2WD does the same. I found that I had a vacuum leak in the valve cover test port which i plugged (probably broken off by my mechanics helper when he changed my plugs). My fuel alcohol percentage goes up to 35% sometimes even though we can only get E10 here. Kills my mileage and i need to reset the percentage and fuel trims regularly. I use a VXDiag to do this and my PC. This is caused by improper fuel filling procedures. You need to fill up when the truck is already warm and drive for 7 to 10 miles for the ECM to calculate the proper alcohol content. I do not follow this procedure as I do not usually drive that far at any one time (retired).