Modern gassers in HD trucks do not crawl around. OP get what you want. I would steer away from the 6.0 diesel. But other than that diesel or gas can do the job just fine. I am very happy with my V10 and the 5.4 I had before the V10. I am a gasser guy and personally don't like the smell or the mess when maintaining them. I really do not like the fact that if anything diesel related breaks its a $1000.00 plus to fix it.
I am not throwing down on diesel just be informed that any economy you get in MPG may be off set by other cost.
IMHO if your heart is set on a diesel, get one. Nothing any of us can say will change that.
However, a gasser is very capable. The new ones are close to 400 HP and 400 lb ft of tq. I
I think the new Ford 6.2 is rated at close to 15k trailer weight.