Find out for sure that you can wait until the factory warranty expires and then purchase the extended. I was told by a Chevy dealer that I should get the extended prior to the factory one expires. I was about 15 days prior to factory expiring and purchased the extended from a Chevy Dealer and got a 5 year zero deductable. I had purchased a 2014 in October '15 (had been put in service in October 13) and the factory warranty ran out the following August. When I got the truck it had 7200 miles on it.
Good Luck.