Sorry I can't help with the location of the manifold pressure sensor.
At the front of the engine between the engine cover and battery cover there is a small flexible pipe about two inches long and 1.5 inches in diameter. Check that there is not a split in this pipe as a split can cause going into limp mode when the split opens and be ok again if it closes.
What you describe doesn't sound like the fuel pump solenoids. Problems with these causes a misfire under load at around 2500 rpm but doesn't result in limp mode.