Jeremy Lowery

If this is an SLE as titled...then the small end of the shims should be pointing towards the rear. Large end pointing toward front. It angles the rear diff/axle slightly to achieve the correct pinion angle. There were no blocks installed from factory on your model. Your dealership must be confusing it with the previous generation Sierra which had factory 1" blocks. What is the problems that you are experiencing?

Sport I believe. It's a little nerve racking to drill through a $50k truck but all in all it was quite simple.

Installed AMP bed extender. I also have the craftsman toolbox from Lowes. Just peeled the crafstman logo off and stuck it inside. Probably gonna switch out for a BetterBuilt or UWS slim. The craftsman is advertised as slim but it's kinda in between a slim top and regular. It also hit the back of my cab when I had the box pushed all the way to the front of the bed. So it sits about an inch away from the front wall.

Installed a Gentex framless dimming mirror. Spliced in to the glued harness (Violet/White wire) using the provided universal harness. Works as it should. There's homelink versions available for some extra $$.