Grand Canyon, Eastern NPs
C2C,
I can heartily recommend the half-day drive-through loop through the Grand Canyon, exactly as suggested (which is essentially the only route available).
Back this way, be aware of the high elevations and early and severe winter weather in the Smokies. Much of the Blue Ridge Parkway (BRP), particularly the higher elevation segments down that way, are closed much of the winter. Just this week I read of a scheduled closure of a segment near Asheville where bridge repairs will require longer-term closure.
As you head from Knoxville up I-81 towards DC, you can test short segments of the BRP between Roanoke, VA and its northern end at Rockfish Gap and/or all or parts of the Skyline Drive (SD) within Shenandoah National Park. In each case, lower elevations than those here in NC generally mean fewer and shorter winter closures.
Foy