How is the sharpness,type, and quality of your blade? What blade height are you using? You should not have to work that hard. The length of the fence should not matter. Your blade should run dead parallel to the miter slot, I like my fence open about 1-2/1000 on the outfeed end. Have no scientific evidence it makes a difference, just the way I was taught. Blades can start to deflect when they get hot, which would be the end of the cut. I would make sure you have a good, stable, sharp blade. U have always used Forrest Mfg. blades, the Woodworker II is a good choice. They are pricey but you will have it for ten years. I would also try, if you have not already, raising the blade well above the stock.