Help! My 2008 Yukon Denali XL is seriously screwed up. I am somewhat mechanically inclined but I have to admit I have no idea where so start. Here’s the order of degredation; yesterday while driving along just fine, the “service stabibilitrak”, “ traction control off”, and “service suspension” lights all came on. At the same time the tranny shifted down to about 3rd I think, RPMs jumped up to about 3k as I was going about 40 MPH at the time. I slowed down to a crawl and pulled off the road as soon as I could. I shut the car off, waited about 5 minutes and restarted. It behaved for the rest of my commute to work. Later in the day on my way back home same thing happened only this time it would not go away even after letting the car sit off for a few minutes. I limped it home at about 25 MPH as not to run the RPMs too high and parked it in the driveway. I figured that I would hook up the scanner in the morning and check for a bad wheel speed sensor or TPS etc. This morning I attempted the start the car, scan the codes etc.... however now it won’t start at all. No clicking no cranking, nothing . Although, the voltage gauge shows 12 v and every other electrical accessory works just fine with the ignition in excessory position. ( except for the power lift gate, not sure if that is a related issue or not but it has always worked until now)So, the scanner cannot connect, the POS won’t start, and I need a drink. Help !