Does 421,560 count? Just traded in a 1997 f 150 gas 5.4 and it was still running good. Just got tired of driving the same truck after 18 years. If you maintain them they all will last.

The OP stated he plans on pulling this boat daily !!!!!!!!!
No gasoline engine will tolerate that for very long....
I haul everything with my truck on a pretty regular basis..
7000 - 8000 lbs of hay, 3-4 working horses in a trailer, or my boat ...
I'm knocking on wood as I say, .... IT HAS NEVER LEFT ME STRANDED !!!!!!
But, it did limp home one day, due to clutch slipping.....

What your looking for when towing is low end torque. As someone already stated, gas engines tend to struggle more at higher speeds and have to downshift. Take the ram 1500 for instance. The 5.7 hemi makes its max 409ft lbs of torque at 4400rpm. Where the eco diesel makes its max 420ft lbs of torque at 2000rpm. It's the same principal with the ecoboost f150. The 3.5L ecoboost makes its 420ft lbs of torque at 2500rpm. Most Diesel engines hit peak torque below 2000rpm which is why they tow much better IMO. That being said today's turbo charged Light duty trucks in both gas and diesel variations are much better than they have ever been. OP, I would try to talk to some dealers and see if they will let you take one on an extended test drive so you can see how it pulls your boat, that's really the only way you will know for sure. Looks like they have some good deals on the Rams right now

http://m.autotrader.com/cars-for-sale/vehicledetails.xhtml?listingId=429836416

http://m.autotrader.com/cars-for-sale/vehicledetails.xhtml?listingId=427488991

I run a 2011 F250 with the 6.2 gas engine. I currently pull a completely loaded 19' Lund with Honda 150 strapped to that. I pulled the boat 5k miles this past summer and it pulled it ok. You would think it would pull it easy enough and for the most part it did. Hills would make that 6.2 work hard and even down shifting it into 4th a more than a few times. I kind of regret not getting a diesel but couldn't justify the 7-9k add on at the time. My average mpg for the 5k miles was about 10 mpg. Far from being impressive. The trip was more of a one off thing so i wont be doing very many of those. Locally the 6.2 motor will suffice for my needs. If you consider pulling lots of miles then think hard about a diesel. As someone before me mentioned.... torque. As far as the ride, it was comfortable and the brakes never felt mushy etc. Best of luck on your search.

Don't fear a gas engine, they will live when worked too. Most ranchers around here drive gas vehicles and have no problems getting 200,000+ miles on an engine. They hate diesels for the weight and maintenance cost and the fact the stop and start them many times a day. They all make the little 90-100 mile one way trips to the sale barn 3 days a week with a 28' to 32' cattle trailer. Most oilfield pumpers run gas for the same reasons.

The issue with gas engines in 2500/F250 is that you can literally see the gas gauge drop. For a heavy truck, a diesel engine is the way to go.

Go with the Ford F-250 all day! -:)