Actually even US 129 east/south of Deals Gap is a great ride. Just about any road that runs across it or cuts to a numbered road. Deal's Gap has too much traffic and was very heavily enforced on the weekends when I was in the area last summer and fall. You need to experience it though as it is one of those roads that is really one of the best in the east.
Like Joe said you need to run the Skyway. The best part of that is you can run it out and back and you will think it is a different road. Too much going on to take it all in on one direction only. I did the Skyway last season for the first time. That whole area is great riding. Almost all of the runs in that area are not short as the roads are long in miles and time. Franklin is a good area to be based out of. I was running out of Atlanta and every day we went north to the mountains it was a good haul getting to the 'good stuff'. However, that was where I was 'working'.. when I wasn't riding
I believe that most of the roads that parallel I-81 are good for riding, even US-11, if you get back on to I-81 anytime you get near a city of more that 10,000 population. Coming down from PA you can also take US 250 to miss the Maryland and upper Virginia I-81 sections. I think that is a nice ride also and virtually no traffic..
IMHO, to go from PA to that area around Smoky Mountain NP there is only one M/C
way.. and the is the Blue Ridge Parkway. It can be tough if the weather does not cooperate but you just can't beat 550 miles of road without a stop sign.. great views and twisty roads..
Last year I did the BRP top to bottom and it was perfect weather. I must have been up there more than a dozen times and this was the first time weather or traffic was not a problem. I only came off the parkway to sleep..
IMO, I-81 between PA and Tenn is an awesome ride compared to I-70 and I-80 anywhere
between the Mississippi River and the Rocky Mountains.. I don't know about beyond the Rockies..