IMO, do NOT take exit 1, 421. That 20 miles to Duffield is curvey, narrow and hilly. If you run into any traffic it will be a lot slower. I have clocked every route you can take, several times. I go all the way to I26 to Kingsport exit 57, 23 to Weber City. Be sure to take the 23/58/421 bypass around Gate City, into Duffield and then 421 into Harlan. It's only an few miles further than exit 1 and easier and faster. The only real problem is the pull out of Duffield. It's straight and the grade isn't too bad but it's a long pull, about 4 miles. Watch for the 421 right turn about 10 miles from Duffield off of 58, it comes up on you quick. There is one short stretch just before you hit the four lane into Harlan that is super curvey and narrow, kinda like the curvey part of Nantahala Gorge going to Tellico. There is one hair pin curve, 15 mph, heed the warning, I've been off the road there! Just my .02 after 12 trips over there and back! You shouldn't have any problem with your rig if you're careful.