What would cause my Ford F-150 5.4L to surge and stall at times?

My truck has surged when taking of real slow. When I go up steep grades the check engine light will come on and stall. Then I would crank it back up and it will run ok for a few days and do it again. The last time the engine light came on it stayed on for 1.5 days and went off. I took it to a local mechanic to see whats wrong with it. He said there were no codes to be found. So I asked him to go ahead and change the fuel pump. It ran ok but it started the same issues. It seems to only do this when I try to pass another vehical or climb steep grades. It also seems when I do give it gas that the motor is not performing at its best. Seems like there is a restriction.