My problem started a month ago: When I need power to climb steep grades the truck runs great for maybe 1/4 mile them suddenly looses power, so much that the motor returns to idle and I have to crawl up the hill. After I try to make it,(I always turn around) I notice my brakes feel like there is no power booster for about a mile while going downhill, then the brakes feel fine again. I can feel the pressure build back up. I never have a problem around town, it only appears after I begin to ascend up a hill. I changed the fuel filter, fuel pump, brake booster check valve and hose. After I changed the Fuel pump the truck did run better and I made it further up the hill, but eventually it stalled again. Any help would be much appreciated.