What could cause my 97 Nissan Pathfinder to stall after 30 min of running fine?

Hello, I have 97 V6 Nissan Pathfinder that starts, idles, and runs great but after about 30 minutes it stalls as if someone turned off the ignition. Sometimes I can start it right up again and sometimes I need to wait. When it does not want to start right up, I have verified that it does have spark and it does have gas pressure to the injectors. A year ago I had my distributor replaced when the car died on me on a drive. But until now I have had no issues. It does have an engine code for a dirty catalytic converter but the engine runs great and I have not lost any power. Any guesses? :-(