If the light was flashing, then you had a misfire. Now, I would normally ask when the last tune up was done, but I don't think the plugs are causing the issue you described. Regardless, I would like to know what code was set in the computer when the light was flashing. It will better help me determine where I feel the problem may be coming from.
Since the problem seems to occur when the engine is under a load (passing, climbing a hill...), the first thing I question is the fuel pump. Have you checked fuel pump pressure?
https://www.2carpros.com/articles/fuel-pump-pressure-and-regulator-test-video-all-cars
The above link is a video showing how to do it. I feel we need to start there to see if the pump is producing pressure that is within the manufacturer's specs. If you don't have a fuel pressure gauge, contact the local parts stores and see if they will lend or rent one to you. NOTE: This video shows how to check pressure, the pressure regulator, and fuel pressure drop off. Check all and let me know what you find.
Monday, January 6th, 2014 AT 9:45 AM