traveling from Port Huron Michigan to Nashville. I had a scary experience a few years ago driving to Charleston...now I am terrified of encountering steep grades...and yes I know interstates do not have what most of you would consider steep...but for this flat lander I77 was terrifying. I am thinking I65 may be flattest route? Any info on any steep grades I may encounter would be greatly appreciated!! Please help calm my nerves I want to enjoy this road trip without worries. Thank you!