Oh Dallas. I'm about ready to admit defeat. In a story I did calling for hoagie suggestions to satisfy my East Coast carpetbagging cravings, many chimed in citing Jimmy's, The Great Outdoors, Biladelphia, Great American Hero and more. I asked for shredded lettuce, a sturdy roll and high-quality meat. Commenter BigJonDaniel nailed it, though; I'd have to settle for two of three.
The issue you will have in Dallas is the bread. It's a poor bread town. Jimmy's comes closest, but theirs is more like an "Italian" from Maine than a Hoagie. Great Outdoors is a stand by, mainly because they bake their own bread, but the bread is not as robust as the roll you describe...
I ate at several of your suggestions. I found lots of great cold cuts, and shredded lettuce is obviously an easy find. But we've gotta have a chat about bread in this town.
I'm not ready to go as far as Jon and proclaim Dallas' bread scene broken, but I think many area bakers are leaving something on the table. Even the sourdough I had during a fine dining experience left a little to be desired. Where's the chewy structure and the crunchy flaky crust I crave?
Many knee-jerk to blaming the water, citing the superior water supplies in stronger bread cultures like New York, Philly and San Francisco. But any master baker worth will tell you that water is minimally important. Flour quality, dough handling and baking conditions are what give bread its taste and texture. The bread in Dallas is the way it is because of how Dallas bakers bake it.
It is possible the heat could be affecting things, if area bakeries don't have good climate control. But that seems unlikely. You don't open a bagel shop in hell without calling the HVAC guy first.
Perhaps expecting coastal qualities in a Dallas sandwich is just too much to ask. Regional cuisines are usually better when closest to their point of origin. I wouldn't ask a Dallasite what they think of Tex-Mex in Jersey City, so why ask Aters where to land a good hoagie?