I am assuming you mean I95 as there is also I85 in SC.
Cheap fuel is all around SC partly due to taxes but also because we have a nice pipeline taps which reduce transportation cost.
1.67 for gas isn't cheap in my opinion. Lately I've been driving by 1.63 and know of places below 1.60.
On I26 west bound, recommend something around MM 8 give or take a few exits depending on the gas stations moods. Exit 28 is also usually a good spot.
Cheapest gas in the state for last several months has been in the smaller city of Greenwood.
Don't forget, your Good Sams Club is good for 3 cent discount at Pilots. A lot of Sam's Club is 3-5 cents cheaper than nearby stations when it is for members only.