Engine misses when going up hills

Never had a bit of problems with this automobile, then out of no where it started to miss when going up different grades, of course more gas pedal is used and that extra strain on climbing hills seemed to cause the problem. On level roads, the car runs fine. Note: the engine light is on steady. Thinking, some moisture in the tank, may be causing the problem, but that theory was eliminated. Any ideas to this type of problem would be appreciated.

Regards:
BIGmidget