2001 Ford F250

i have a 5.4 liter f-250, when i am driving it seems to loose power. i will push the gas and it goes but acts like it wants to stall or almost like it is running out of gas. i literally have to put the truck in nuetral and turn it off and restart it and then it goes fime for awhile and then it acts up again. it does it at high sppeds and low. i was thinking the fuel pump relay,, but i dont even know where to find it.
thanks