I like Murphys USA at Wal Mart and with a Wal Mart Card you save $.03 pergallon; however, not all Murphys have Diesel but most do, check your Road Atlas.
QT's are great too, in our area we have both so the competition is great.
I am very cautious about smaller fuel outlets because of old fuel. Pilot's are almost always $.02 per gallon more than a J in the same area.
I have actually fueled at a Murphys with my one ton crew cab dually with my 33' fifth wheel,tight but can be accomplished.
Also if your on the net while traveling gasbuddy.com gives good info for most areas and they have Diesel prices listed.
Big Al
Branson MO
Retired Navy