We live in Va, just off I-81 and I-64, and have traveled both, and I-77 alot.
From I-81 to I-95, using I-64 no long grades accept from mm 96 to mm 101, you'll go over Afton Mountain, but it's not bad at all.
From I-81 south down to I-77, no bad grades at all.
On I-77 south from I-81, just your normal 3-4% grades every now and then. Only bad spot is I-77 at the Va-NC state line. It's a 5-6% grade---but downhill (going north it's 5-6% uphill). Once in NC no really bad grades, but around Charlotte the interstate is very busy, and road surface is crummy.
I-81 and I-77, road surface is quite good...just got back from Fancy Gap KOA and took that route back. If you need a real nice campground while on that route, Fancy Gap KOA, I-77, exit 8 is beautiful. Real nice KOA in Wythville, Va, off I-81.