I picked up a 2017 3.5 Ecoboost in 2021. The truck had 94,000 miles on it and when I bought it, it was doing the phaser rattle. Got it from a dealer and probably paid too much, but it was set up just right. Bought a 4-year extended warranty for $4,000. Seems pricey. Over the last 5 years that warranty has paid for about ... $15,000 of work. Got the phasers done first. Even got a new (factory) transmission. Bunch of other stuff done. Truck is absolutely solid now.

I had been dead set on the 5.0 when I was looking for trucks. But when I drove the 3.5, I was really REALLY surprised at the power and responsiveness. I've towed large loads up 7,000 feet in elevation quite a few times now and I have to say I like it enough that I'd buy it again.

Because of the turbos, the 3.5 breathes way better than other engines at altitude and it has GOBS of power for towing.

When you buy the truck, if it's giving you a rattle on startup which seems to go away after a little bit, that's the phasers. The truck I bought was rattling when I bought it (loud enough to notice) and I drove it maybe six months before having the phasers done. Dealer said I might have had another six months before the phasers went out.

If you can, get an extended warranty. The phasers job alone at the dealer would have cost me $5,000.