One suggestion for when you leave Dallas, take 20 east over to Marshall TX. and make a stop at Marshall Pottery. If that is remotely in your interests they have some neat things from coffee mugs to water urns, bowls, flower pots etc.
Now on to TN.....Memphis has Beal street, Graceland, Gibson Guitar Factory, and The Pyramid, which is now a HUGE Bass Pro store. DO NOT wander away from the "tourist" areas while there. Memphis is a rough place, it has the highest crime rate in the state. Nashville is nice but not a whole lot to do IMO with the exceptions of The Grand Old Opry, Country Music Hall of Fame and the downtown area proper with all the great restaurants and shops.
Jamestown is a good day trip (not very far)for Dollywood BUT a day trip is not going to give you the true Sevierville/Pigeon Forge/Gatlinburg experience. Dollywood is a great park really but be prepared for a pricey ticket at $58 bucks per person. There is really SOOO much to do in the area that a few days are required to see much of anything. Lots of great campgrounds in the area too.
Jamestown is also close to Crossville which has the Cumberland County Playhouse. It is a wonderful place to see a stage production play. Look up their web site to see what they are performing when you are going to be visiting your friends.