Sheetz is based out of Altoona, Pennslyvania. It branched out from a dairy business and as a local mom and pop version to 7-11. It is privately owned and family run.
It has only two "true" truck stops that I know of ...
Dubois, PA and Mount Jackson, VA
The furthest south Sheetz I know of is Mebane, NC off of I 85. I was shocked because I thought it ended at Colonial Heights, VA near the intersection of I 95 and I 85.
Yes, I did pass that Sheetz in Wytheville, VA on my way to Dollywood. That's the furthest south one on I 81.
Most Sheetz I know do have diesel but it's auto diesel and also I don't think the trucks can fit under most of their fuel island canopies.
If you want to ask them to expand from those two truck stops and "go for it" ...