I'm a died in the wool GM guy, but in all fairness GM has had A LOT of issues with there 4l60e's. I had to have a valve body done in mine around 80K, my in-law bought a 1/2 ton GMC new in 2000, at 60K he had to have the transmission gone through because a few clutch plates disappeared and some other bad stuff happened, my brother smoked his, twice in his Tahoe, and those are just the ones I know personally.
On the flip side, we had a 2001 Suburban 1500 4 X 4 until 3 years ago. I ran synthetic ATF (and everything else), we sold it to my neighbor 3 years ago with 260,000 miles on it and they drive the berjeebers out of it. It's got to have 300,000 + on it by now. And that's the original 4l60E.
155,000 on our 08 Burb 1500, same transmission and it's rock solid.
All that said, whatever truck you by make sure it's got a towing package that includes a transmission cooler. Taller gears like 3:73's are a bonus.
I don't know a whole lot about the Ford EcoBoost V-6, but I have seen those things handily tow large skid Steers on heavy duty trailer, 30 travel trailers, etc. Really impressed how they get off the line with big loads. That said, how long will that small V-6 last pulling like that.