I'll start off with the basic info: 2004 Suburban LT, 4x4, 5.3, 179,000 miles. We took a recent 3,000 mile road trip from Denver to the Gulf coast of Texas (Corpus Christi.) For the 1100 miles down and the 1100 miles back, we were pulling a 3500lb travel trailer (R-Pod 179.) On this trip, 3 separate issues appeared, and I'm wondering if they might somehow be related: 1. The night before we left the truck started throwing a CEL. I have a code reader (Scangauge II) and the code that showed up was P0161, which my internet research shows is an oxygen sensor. I reset the CEL, and it would stay off until I turned off the engine and then turned it back on, and when I did the code would reappear without fail. 2. Once on the way down and twice on the way back up, the alternator light came on and the DIC displayed a "battery not charging" message. This lasted less than 30 seconds and the light went back off. Both times when this happened we were connected to the trailer and towing at highway speeds. The trailer does have a 3 way refrigerator that we run on 12v DC while in motion (once we are stopped we put the fridge on propane if we don't have hookups or 120v AC if we have electric hookups, which we did on this trip.) EDIT: I should note that I replaced the alternator early last year (April 2017) when it failed, so the alternator is a rebuilt unit from an auto store. It is a 145a alternator. 3. When driving through a heavy dust storm, I tried to put the HVAC system onto "recirculate" to keep dust out of the cabin. When I tried this, the light on the "recirculate" button would flash several times and then go off. Any idea what these issues are and whether they might in some way be related?