I've been putting 30K+ every year on my 2009 F150 5.4.

About 12K of those miles every year is pulling a 12 utility trailer or an enclosed 10' trailer. So, maybe 1/3 of my miles.

As I think about looking for a new truck, should I be looking for something with higher torque, better puller, whether that be a diesel or ecoboost or should I not be thinking that way?

That 5.4 pulls good but you know when you are hooked up to a trailer. Traveled to ND this past year with a buddy with a power stroke and an enclosed trailer and when I drove, I would forget that thing was back there. Maybe that's the way I need to go?