Research, research, research... which is why I started this thread. And thank you to everyone who responded so far; the more info, the better.
The step in height is the big MDT killer, and any modifications just raise cost. For pulling 17,000 GVWR (with no plans to go heavier) a 3500 will work for us; 3 axle toy haulers weight more, and I rarely see anything but LDTs pulling them, though the guys pulling them with 3/4 trucks should really be reading all the MDT responses; I actually saw a Ford Raptor pulling a 3 axle Raptor over Labor Day weekend heading I10W near exit 5 in Florida.