Grapevine Mills is definitely your best bet. It's less than 2 miles from DFW airport, has a ton of retails/outlet shops, Virgin Records, a bookstore (not a great one), a multiplex cinema (great way to beat the heat!) and Rainforest Cafe' (themed restaurant with overpriced food but cool interior). Also, the Bass Pro Shop (check out the website - my description wouldn't do it justice!) is in front of the mall on the access road, as well as many other restaurants. Grab a cab and tell the driver to pick you back up at the same place in a couple of hours!
This is, of course, assuming, you aren't going to have to take your luggage with you!!
If you REALLY want to do something unique to Dallas, check into the possibility of somehow getting to downtown Dallas to go up into the "Dandelion" or the Hyatt Regency tower, which has a revolving restaurant at the top, giving you a 360 degree view of the Big D. I'm not sure, but check out the DART Rail possibilities (www.dart.org) to see the timetable to and from DFW to the West End area.
Oh, and try to stay COOL!! It's hot here right now!
28 years of living in and around Dallas, and having friends and family members visit for various lengths of time...