First of all, welcome to the forum! You'll find many friendly, really helpful (smart) folks here!

Okay, about the tree...some questions - is the tree planted at exactly the same level as it was originally? Make sure it is no more or less deeply planted than it was. Was the new hole big and deep enough to allow plenty of room for the roots to spread? A very wise teacher of mine always said "Dig a $50.00 hole for a $10.00 plant" Did you firmly "tamp" the soil after planting, and water in well immediately to remove any air pockets? Air pockets will dry the roots and prevent them from taking up water properly. What I do is fill my planting hole with water, let it drain, put in my plant, backfill with good soil, tamp well, and then water in really well. Is the tree in full sun? Tulip Poplars do very well in full sun, but until it's over the stress of being moved, it may benefit if you fashion a "shade" of some sort for it to keep the sun off during the hottest part of the day.
Most plants will show some signs of stress (wilting) after being moved, especially during the summer. That may be all you are seeing.
You are definitely doing the right thing by watering. All plants need plenty of water after being transplanted until they are well established. With trees, sometimes this takes as long as a few months.

Well, there's a few things to check, I hope it helps you out! Tulip Poplars are beautiful, (they're our state tree here in TN) definitely worth any extra trouble. I have one right in the middle of my front yard, it's 50 yrs old, and about 70 ft tall. It's the first tree in the neighborhood to bud in the spring, (the neighbors check it to see when spring's coming) and the blooms are gorgeous! I always cut a few, leaves and all, and put them in a vase. They last a really long time!

Anyway, if you have any questions, ask away, and let us know how your tree does.

I love these trees too, that's why I never pulled the darn thing out of my flower bed for the past two years because I knew it would be nice to transplant. We have an old one in our back yard that the kids love to climb and I truly enjoy its flowers.