I have a 2017 el that was also a rental prior to my purchase,with 56k on it. I've only put 3,500 miles on it since August. The only issue I've had is that when park it with the front end higher than the rear end(parking spot with a decent grade), then water from rain overwhelms the 2 rear sunroof drains and water has poured into the vehicle from the 2 central roof air vents..... I'm gonna run some trimmer line through the drain lines and that may solve the problem, but I cant imagine that they are clogged. If you don't have a sunroof, then this shouldn't be an issue. For more info on mine and similar leaks look at the "2017 Water Leaks" thread.
I average 13.8 right now, but most of my driving is around town while carrying my wife and 6 kids...so running with more weight than some. My wife took a 1,000mile trip Kentucky and back and got around 17 carrying a full load of passengers and the cargo area full as well
For perspective, this truck replaced my 2001 Chevy Suburban LT with 195,000 miles....had a sunroof and never had a single leak. I guess chevy is better at designing sunroofs/drains.....still miss my Suburban
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