I've not had a good experience with Eco. I get 1-2 mpg less when I keep it in Eco. I have a '21 3.5 eco and after checking fuel economy by hand over a month, filling up weekly and alternating Eco and Normal weeks, I just keep it in Normal now.
I am looking for a locking, removable tonneau cover for a '21 with a 5.5 bed. I am considering the Undercover Armorflex but it's warrantied for only 5 years. I was pretty set on it until someone pointed out the Line-X has their LXP with a limited lifetime warranty. Is Undercover still the better...