As you're new to this, do you have any friends or family with large trailers and similar trucks? It would be good to get a feel for how a base model gasser pulls compared to a modern newer diesel.
Not something you can discern just with test drives, because the 6.2 will feel very powerful and fast with nothing hooked to it.
Or to put it this way, if I was hauling even a small 5ver alot and someone offered to trade me my 13 year old 175k mile diesel pickup that is running about 500hp/1000ft lbs for a 3 year old equivalent 6.2 gasser truck with low miles, it would be a hard pass!