Lowest elevation route

Try this tool.

google 'lowest elevation route'

I-70 has nothing too high but don't know how high is too high for you.
bumpy

On google maps start in Kansas then go to Nashville and then to Arlington. I-81 runs up the valley between the mountains.
Something Like this Kansas to Arlington

I-40 up to I-81. Highest point will be less than 2000 feet.Crab Orchard is about 1600 or so. Going across upper Maryland, Oldmans tool says about 2800 or so.

How far out of your way are you willing to go. Drop down to I-10 and follow it to I-95. You will be close to sea level all way.

Only real high elevation is in Virginia. Long hills but low altitude compared to colorado

High elevation in Virginia is 2000 ft. Come over I70-I270. These are not mountains they are hills. I live here and have driven all 48 lower states in a truck.