This fall we were in South Carolina. They are in dire need of Sheetz down there. As much as I loved Myrtle Beach, I needed my Sheetz. Stopped at the first one we found half-way up 95 in North Carolina. Vacation without Sheetz is culture shock to the extreme.
The only Sheetz location in Durham is in southeast Durham county (near RTP). There is most definitely a market between that location and the next closest location (Mebane, NC). A location in North Durham or between Durham and Chapel Hill would serve a distinct set of customers that include commuters, college students, and drivers along a busily-traveled stretch of I-85.