We went with a 1T over 3/4 for the reasons stated above. When comparing the price of a F250 to a F350T (no real difference), the fact that maneuverability is a wash they are the same, not being near the limit on payload, it just seemed like a no brainer. It made me question why the F250 exists. If the price is almost the same, The entire truck is the same with the exception of increased payload, why wouldn't you buy a 1T? I only know the Ford so I can't say if Chevy and Dodge have the same comparisons.
As far as engine, I looked at the new Godzilla in the Fords. Respectable numbers for sure. Mileage is a killer. I went with the reliable 6.7 turbo diesel and I couldn't be happier. Married to the 10 spd tranny I am getting 21 mpg + on the highway (16-18 towing our FW). I think the gas engine gets about half that. Understanding you pay quite a bit more for the diesel, but in my experience they hold their value longer and just last longer - but it's all relative. But the Godzilla isn't a bad choice by any means. It's a terrific engine.