My Check engine light for my Duramax is also on just like yours is. I haven't checked the code yet. Have you? Oh, I love my exhaust break too! Really cool!
I forget what it was.. I did clear it with Torque 2 Pro on a Bluetooth connection. That truck is a North Idaho set up we can't discuss... I borrowed that from my business partner. My 5.3 truck was having 240 degree trans temps and smoked the brakes going down. 5 days a week commuting with a 5000lb enclosed welding trailer was going to kill it. I found a 2006 LBZ dually quad cab eventually but it does not have the engine brake. I found some info about the road from a bike site.. "The climb is about 2,600 feet over nine miles. Starts at 2200 feet and goes to 4800. It’s actually 8.9 miles. Just under a 6% average but it’s more difficult than a uniform climb at 6%. There are multiple sections at 8-10% and the grade changes often enough to make finding a rhythm difficult. Even so, it’s beautiful. The view from the top and from the highest hairpin look out onto the lake and are spectacular. Great descent with several sections where you can fly." pjammcycling.com/climb/665.Schweitzer%2520Mt.%2520Road