It will sound a bit vague, but my co-worker "blew" his transmission in his Silverado (ZL1) on the way back from West Texas. Truck had around 70K on the odo, no fluid changes on the tranny. Don't have many details but he said it was shifting "funny" first, then threw CEL and finally gave up completely. Luckily it happened next to Chevy dealership in Austin. Waiting to hear back from them since his warranty expired (despite the fact he had an extended warranty but they for some reason trying to deny this fact). I'll post more as i get details from him.