This is my first post. I've read Motor Oil University, and a couple of searches have yielded nothing. I just bought a used (20,300-mi.) 2014 Chevy Impala LT sedan with a 3.6-L V6 engine. The recommendation is for 5W30 GM oil only. I don't have the owner's manual at hand to relay the details of the other specifications for the oil. The GM oil costs $7.95/quart, and apparently no one has developed or marketed a generic substitute for it yet. I live in the Houston area and drive hard and fast when possible. My weekday commute is about 17 miles one-way, with a mixture of stoplights, internal highways (posted 55 mph, traffic flow sometimes 80 mph), and often gridlock. Before shifting into gear, I religiously let the engine warm up until the rpm falls as far as it's going to. If crucial details are missing here, please ask for them. Questions: 1) Must (should) I stick with the GM oil, or can I use dino oil at all? 2) If I use other-than-GM oil, will my engine last for 100,000 miles? The mechanic who has done my conventional oil changes says that he'd be loath to use anything but the GM oil, because in the event of an engine problem, tests are done, and if unauthorized oil is found to have been used, warranties become void. Thanks in advance for your blunt, informed answers.