So I called the number on the card. It turns out that the card only works on the diesel pumps in the truck lanes at Road Ranger stations.
I was told that Road Ranger is a 'dealer' for Pilot Flying J and only services diesel at those locations. At 'regular' Pilot and Flying J locations, the card should work at all pumps. I guess the key is to make sure the pump you select has the Pilot or Flying J logo on it. At the Road Ranger stations, the gas pumps did NOT have either logo, only the diesel pumps in back had the Pilot logo.